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You are here: Home / Deltek Cobra / Setting up an Oracle ODBC Driver and Data Source June 15, 2012 By TheCobraGuy This article explains the steps including tnsnames.ora configuration. Does anyone know of any ODBC drivers available for Oracle on Linux?

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This chapter contains the following sections:

Topics:

21.1 About Oracle ODBC Driver

What is ODBC?

Open Database Connectivity (ODBC) provides a standard interface that allows one application to access many different data sources. The application's source code does not have to be recompiled for each data source. A database driver links the application to a specific data source. A database driver is a dynamic-link library that an application can invoke on demand to gain access to a particular data source. Therefore, the application can access any data source for which a database driver exists.

The ODBC interface defines the following:

A library of ODBC function calls that allows an application to connect to a data source, execute structured query language (SQL) statements, and retrieve results.
SQL syntax based on the SQL-99 specification.
A standard set of error codes.
A standard way to connect to and log in to a data source.
A standard representation for data types.

Figure 21-1 shows the components of the ODBC model. The model begins with an ODBC application making a call to the Driver Manager through the ODBC application program interface (API). The Driver Manager can be either the Microsoft Driver Manager or the unixODBC Driver Manager. Still using the ODBC API, the Driver Manager makes a call to the ODBC Driver. The ODBC Driver accesses the database over a network communications link using the database API. Figure 21-1 shows an ODBC application accessing three separate databases.

Figure 21-1 Components of the ODBC Model

Description of 'Figure 21-1 Components of the ODBC Model'

21.2 For All Users

Topics:

21.2.1 Oracle ODBC Driver

Topics:

21.2.1.1 What is the Oracle ODBC Driver

The Oracle ODBC Driver enables ODBC applications on Microsoft Windows, as well as UNIX platforms like Linux, Solaris, and IBM Advanced Interactive eXecutive (AIX) read and write access to Oracle® databases through the ODBC interface using Oracle Net Services software.

The Oracle ODBC Driver uses the Oracle Call Interface (OCI) client and server software to submit requests to and receive responses from the data source. Oracle Net Services communications protocol is used for communications between the OCI client and the Oracle server.

The Oracle ODBC Driver translates ODBC SQL syntax into syntax that can be used to access the data source. When the results are returned from the data source, the Oracle ODBC Driver translates them back to ODBC SQL syntax.

Figure 21-2 shows the Oracle ODBC Driver architecture as described in the preceding paragraphs.

Figure 21-2 Oracle ODBC Driver Architecture

Description of 'Figure 21-2 Oracle ODBC Driver Architecture'

* The Oracle ODBC Resource data definition language (DLL) file (sqresxx.dll), where xx represents the language abbreviation, contains all pertinent language information; the default resource file used is sqresus.dll.

For more information about the OCI client and server software, refer to the OCI documentation.

21.2.1.2 New and Changed Features

Topics:

New Features for Oracle ODBC Driver Release 12.1.0.1.0

Features of the Oracle ODBC Driver Release 12.1.0.1.0 software for the Microsoft Windows Server 2008, Windows Server 2008 R2, Windows 7, Windows 8, Windows Server 2012, Linux X86-64 (32/64 bit), Sun Solaris SPARC64 (32,64 bit), IBM AIX 5L (32,64 bit), Sun Solaris X64 (32,64 bit), HPUX IA64 (32,64 bit), ZLinux (32,64 bit) operating systems are described as follows:

Oracle ODBC Driver now supports 32 KB data columns with VARCHAR2, NVARCHAR2 and RAW data. See Oracle Database PL/SQL Language Reference and Oracle Database SQL Language Reference for information about creating 32 KB columns.
New parameters in the odbc.ini file or connection level attributes:
- SQL_TRANSLATE_ERRORS = {T|F} [Default is F (false)]
  Any migrated third party ODBC application, which is using the SQL Translation Framework feature, expects that errors returned by the server to be in their native database format, then users can register their translation of errors with the SQL Translation Profile in Oracle Database running in SQL Translation Framework mode. After error translation is registered, then ODBC application users can enable this option, SQLTranslateErrors = T, to receive native errors according to their registration.
  For more information on SQL Translation Framework, see Oracle Database Migration Guide, in particular information about SQL Translation Framework Architecture and Overview, Translation Framework installation and configuration, and migration examples.
See Table 21-5 for more information.
Oracle ODBC driver now supports executing a stored procedure, which can return implicit results without using RefCursor. This support eases any third party ODBC application, which migrated to Oracle and wants to use this same functionality that was provided by their previous vendors.
See Oracle Database Migration Guide for more information about implicit results support by Oracle Database.
Extended support of SQLColAttribute() field identifiers to support Oracle Database auto increment feature. You can use this feature by including Oracle ODBC driver specific header file sqora.h in the application. See Oracle Call Interface Programmer's Guide for more information about auto increment:
- SQL_COLUMN_AUTO_INCREMENT
  Starting from Oracle Database 12c Release 1 (12.1.0.1), Oracle supports auto increment columns so the Oracle ODBC Driver has extended the same support through the existing SQLColAttribute() identifier SQL_COLUMN_AUTO_INCREMENT. This property is read-only and returns SQL_TRUE if the column is auto increment; otherwise, it returns SQL_FALSE.
- SQL_ORCLATTR_COLUMN_PROP
  Starting from Oracle Database 12c Release 1 (12.1.0.1), Oracle ODBC Driver supports a new driver specific field identifier SQL_ORCLATTR_COLUMN_PROP, which returns the attributes of the column. This identifier returns SQLULEN value, which has all the column properties, shown as follows:
ODBC APIs supported in Oracle Database 12c Release 1 (12.1.0.1)
- SQLMoreResults()
  Implements ODBC support for implicit results. See Table 21-7 in Section 21.4.11.2, 'Implementation of ODBC API Functions,' and http://msdn.microsoft.com/en-us/library/ms714673(v=VS.85).aspx for more information.

New Features for Oracle ODBC Driver Release 11.2.0.1.0

Features of the Oracle ODBC Driver Release 11.2.0.1.0 software for the Microsoft Windows XP, Microsoft Windows 2003 Server, Microsoft Windows Vista, Linux X86-32 (RHEL AS 4,5), Linux X86-64 (RHEL AS 4,5) (32/64 bit), Sun Solaris SPARC64 (9,10) (32,64 bit), IBM AIX 5L 5.2 (32,64 bit), Linux IA64 (64 bit), Linux on Power (32,64 bit), Sun Solaris X64 (64 bit), Hewlett Packard Itanium (32,64 bit) operating systems are described as follows:

Prefetching of LONG and LONGRAW data
Oracle ODBC driver is enhanced to prefetch LONG or LONG RAW data to improve performance of ODBC applications. To do this, the maximum size of LONG data (MaxLargeData) must be set in the registry on Windows (you also must add the registry key MaxLargeData in the data source name (DSN)), and set this manually in the odbc.ini file on UNIX platforms. This enhancement improves the performance of Oracle ODBC driver up to 10 times, depending on the MaxLargeData size set by the user. The default value of MaxLargeData is 0. The maximum value for MaxLargeData that you can set is 64 KB (65536 bytes).
If the value of MaxLargeData is greater than 65536, the data fetched is only 65536 bytes. If your database has LONG or LONG RAW data that is greater that 65536 bytes, then set MaxLargeData to 0 (the default value), which causes single-row fetch and fetches complete LONG data. If you pass a buffer size less than the MaxLargeData size in nonpolling mode, a data truncation error occurs if the LONG data size in the database is greater than the buffer size.
Option for using OCIDescribeAny() for fetching metadata
When an application makes heavy calls to small packaged procedures that return REF CURSORS, a performance improvement can be made by forcing the driver to use OCIDescribeAny(). To enable this option, set the value of UseOCIDescribeAny in odbc.ini to T (True), default value is F (False), on UNIX platforms, and through the registry on Windows.

New Features for Oracle ODBC Driver Release 11.1.0.1.0

Features of the Oracle ODBC Driver Release 11.1.0.1.0 software for the Windows XP, Linux, Solaris, and IBM AIX operating systems are described as follows:

Disable Rule Hint (DRH Connect String)
Added the new connection option, Disable RULE Hint that allows user to specify the option to select whether to use RULE Hint in catalog APIs. The change has been done to increase the performance of ODBC driver for catalog APIs. The default value for the option is TRUE, which means that RULE Hint is not used in catalog APIs by default.
Bind Number As Float (BNF Connect String)
Added the new connection option, Bind Number As Float. By introducing Column Binding for NUMBER Column as FLOAT when column contains float data speeds up the query execution that uses bind variables as FLOAT.
Statement Caching
Added support for OCI statement caching feature that provides and manages a cache of statements for each session. By implementing the support for OCI Statement Caching option, Oracle ODBC Driver performance improves when users parse the same statement multiple times in the same connection. The default value for the statement cache flag is FALSE.

New Features for Oracle ODBC Driver Release 10.1.0.2.0

Features of the Oracle ODBC Driver Release 10.1.0.2.0 software for the Windows 98, Windows 2000, Windows XP, and Windows NT X86 operating systems are described as follows:

Bind TIMESTAMP as DATE (BTD Connect String)
Added the new connection option, Bind TIMESTAMP as DATE, that allows you to bind the ODBC driver SQL_TIMESTAMP data type to the Oracle DATE data type instead of to the Oracle TIMESTAMP data type (which is the default).
MONTHNAME (exp) Function
Added support for the MONTHNAME (exp) function which returns the name of the month represented by the date expression. For example, 'April'.
DAYNAME (exp) Function
Added support for the DAYNAME (exp) function which returns the name of the day represented by the date expression. For example, 'Tuesday'.
Instant Client Configuration
Added support for the Instant Client mode configuration.

Changes for Oracle ODBC Driver Release 10.1.0.2.0

Changed or deprecated features of the Oracle ODBC Driver Release 10.1.0.2.0 include:

Disable Microsoft Transaction Server
Changed the default setting for the Disable Microsoft Transaction Server (MTS) from FALSE to TRUE. By default, MTS support is disabled.
Floating Point Data Types
Changed the mapping of the Oracle data types, BINARY_FLOAT and BINARY_DOUBLE, to map to the ODBC data types, SQL_REAL and SQL_DOUBLE, respectively.
SQLGetData Extensions (GDE Connect String)
Deprecated the SQLGetData Extensions connection in this release. The functionality of this feature is always enabled.
Force Retrieval of Longs (FRL Connect String)
Deprecated the Force Retrieval of Longs connection option in this release. The functionality of this feature is always enabled.
Translation Options Configuration Tab
Deprecated the Translation Options tab previously found on the Oracle ODBC Driver Configuration dialog box in this release.
Release Notes
Renamed the Release Notes file from ODBCRelnotes.wri to ODBCRelnotesUS.htm.

21.2.1.3 Features Not Supported

The Oracle ODBC Driver does not support the following ODBC 3.0 features:

Interval data types
SQL_C_UBIGINT and SQL_C_SBIGINT C data type identifiers
Shared connections
Shared environments
The SQL_LOGIN_TIMEOUT attribute of SQLSetConnectAttr

Table 21-1 describes the SQL functions that the Oracle ODBC Driver does not support.

Table 21-1 SQL Functions Not Supported by the Oracle ODBC Driver

String Functions	Numeric Functions	Time, Date, and Interval Functions
`BIT_LENGTH`	`ACOS`	`CURRENT_DATE`
`CHAR_LENGTH`	`ASIN`	`CURRENT_TIME`
`CHARACTER_LENGTH`	`ATAN`	`CURRENT_TIMESTAMP`
`DIFFERENCE`	`ATAN2`	`EXTRACT`
`OCTET_LENGTH`	`COT`	`TIMESTAMPDIFF`
`POSITION`	`DEGREES`
`RADIANS`
`RAND`
`ROUND`

21.2.1.4 Files Created by the Installation

Table 21-2 describes the files that are installed by the Oracle ODBC Driver kit.

Table 21-2 Files Installed by the Oracle ODBC Driver Kit

Description	File Name for Windows Installation	File Name for UNIX Installation
Oracle ODBC Database Access DLL	`sqora32.dll`	libsqora.so.12.1
Oracle ODBC Driver Setup DLL	`sqoras32.dll`	None
Oracle ODBC Resource DLL	`sqresus.dll`	None
Oracle ODBC Resource DLL for Japanese	`sqresja.dll`	None
Oracle ODBC Driver message file	`oraodbcus.msb`	`oraodbcus.msb`
Oracle ODBC Driver message file for Japanese	`oraodbcja.msb`	`oraodbcja.msb`
Oracle ODBC Driver release notes
Oracle ODBC Driver Instant Client Release Notes	`ODBC_IC_Readme_Win.html`	`ODBC_IC_Readme_Unix.html`
Oracle ODBC Driver help file	`sqora.htm`	`sqora.htm`
Oracle ODBC Driver help file for Japanese	`sqora.htm`	`sqora.htm`
Oracle ODBC Driver Instant Client install script	`odbc_install.exe`	`odbc_update_ini.sh`
Oracle ODBC Driver Instant Client uninstall script	`odbc_uninstall.exe`	None

Microsoft Driver Manager and Administrator Files

See the Microsoft ODBC 3.52 Software Development Kit and Programmer's Reference for the list of files that are installed with Microsoft's ODBC 3.52 Components.

The Microsoft ODBC components are packages in the Microsoft Data Access Component (MDAC) kit. Oracle ODBC driver on Windows has been tested using MDAC version 2.8. This can be downloaded from http://www.microsoft.com/download/en/search.aspx?q=ODBC+MDAC

unixODBC Driver Manager and Administrator Files

See the unixODBC readme and INSTALL files for the list of files that are installed with unixODBC Driver Manager.

The unixODBC Driver Manager can be downloaded from http://www.unixodbc.org/download.html

21.2.1.5 Driver Conformance Levels

ODBC defines Conformance Levels for drivers in two areas:

ODBC application programming interface (API)
ODBC SQL-99 syntax

The Oracle ODBC Driver supports all core API functionality and a limited set of Level 1 and Level 2 functionality. See Section 21.4.11.1, 'API Conformance,' for more information.

The Oracle ODBC Driver is broadly compatible with the SQL-99 Core specification which is a superset of the SQL-92 Entry Level specification. Applications must call SQLGetInfo with the appropriate information type to retrieve a list of SQL-99 supported features.

21.2.1.6 Known Limitations

The following are not supported by Oracle ODBC driver:

ODBC ASYNC interface
Control-C to cancel execution in an application

21.2.2 Configuration Tasks

Topics:

21.2.2.1 Configuring Oracle Net Services

Before Configuring the Data Source, you must configure network database services so there is an entry for each Transparent Network Substrate (TNS) Service Name. To do this, use Oracle Net Configuration Assistant (NETCA).

Using NETCA, you can create an entry in the tnsnames.ora file for each TNS Service Name. NETCA is installed when you install Oracle Net Services.

21.2.2.2 Configuring the Data Source

Note:

The following configuration steps are for Windows users. Unix users must use the odbc_update_ini.sh file to create a DSN.

After installing the Oracle ODBC Driver and Configuring Oracle Net Services, and before using the Oracle ODBC Driver, you must configure the data source.

Before an application can communicate with the data source, you must provide configuration information. The configuration information informs the Oracle ODBC Driver as to which information you want to access.

The data source consists of the data that you want to access, its associated operating system, database management system, and network platform used to access the database management system. The data source for requests submitted by the Oracle ODBC Driver is an Oracle database and supports transports available under Oracle Net Services.

To configure or add an Oracle data source:

After you have installed the Oracle ODBC Driver, use the ODBC Data Source Administrator to configure or add an Oracle data source for each of your Oracle databases. The Oracle ODBC Driver uses the information you enter when you add the data source to access the data. Follow these steps:

From the start menu, select Programs, Administrative Tools, Data Sources (ODBC). A list of installed drivers is displayed.
Click Add in the Create New Data Source window and then select the Oracle ODBC Driver in the list of installed drivers.
Click Finish. The Oracle ODBC Driver Configuration Dialog Box is displayed. You must enter the DSN and TNS Service Name. You can provide the other information requested in the dialog box, or you can leave the fields blank and provide the information when you run the application.
After you have entered the data, click OK or click Return.

You can change or delete a data source at any time. The following subtopics explain how to add, change, or delete a data source.

To modify an Oracle data source:

From the start menu, select Programs, Administrative Tools, Data Sources(ODBC).
In the ODBC Data Source Administrator dialog box, select the data source from the Data Sources list and click Configure. The Oracle ODBC Driver Configuration dialog box is displayed.
In the Oracle ODBC Driver Configuration Dialog Box, modify the option values as necessary and click OK.

To delete an Oracle data source:

From the start menu, select Programs, Administrative Tools, Data Sources(ODBC).
In the ODBC Data Source Administrator dialog box, select the data source you want to delete from the Data Sources list.
Click Remove, and then click Yes to confirm the deletion.

21.2.2.3 Oracle ODBC Driver Configuration Dialog Box

Note:

The Oracle ODBC Driver Configuration dialog box is available only for Microsoft Windows users.

Figure 21-3 is an example of the Oracle ODBC Driver Configuration dialog box.

Figure 21-3 Oracle ODBC Driver Configuration Dialog Box

Description of 'Figure 21-3 Oracle ODBC Driver Configuration Dialog Box'

The following list is an explanation of the main setup options and fields found on the Oracle ODBC Driver Configuration dialog box shown in the preceding graphic. The tabs found on the lower half of this dialog box are described in subsequent topics.

Data Source Name (DSN) - The name used to identify the data source to ODBC. For example, 'odbc-pc'. You must enter a DSN.
Description - A description or comment about the data in the data source. For example, 'Hire date, salary history, and current review of all employees.' The Description field is optional.
TNS Service Name - The location of the Oracle database from which the ODBC driver will retrieve data. This is the same name entered in Configuring Oracle Net Services using the Oracle Net Configuration Assistant (NETCA). For more information, see the NETCA documentation and Section 21.2.5.1, 'Using the Oracle ODBC Driver for the First Time.' The TNS Service Name can be selected from a pull-down list of available TNS names. For example, 'ODBC-PC'. You must enter a TNS Service Name.
User ID - The user name of the account on the server used to access the data. For example, 'scott'. The User ID field is optional.

You must enter the DSN and the TNS Service Name. You can provide the other information requested in the dialog box or you can leave the fields blank and provide the information when you run the application.

In addition to the main setup options previously described, there is a Test Connection button available. The Test Connection button verifies whether the ODBC environment is configured properly by connecting to the database specified by the DSN definition. When you press the Test Connection button, you are prompted for the username and password.

For an explanation of the Options tabs found on the lower half of the Oracle ODBC Driver Configuration dialog box, click any of these links:

Application Options

Figure 21-4 is an example of the Application Options tab found on the Oracle ODBC Driver Configuration dialog box.

Figure 21-4 The Application Options Tab of the Oracle ODBC Driver Configuration Dialog Box

Description of 'Figure 21-4 The Application Options Tab of the Oracle ODBC Driver Configuration Dialog Box'

The following list is an explanation of the fields found on the Application Options tab shown in the preceding graphic:

Enable Result Sets - Enables the processing of Oracle Result Sets. If Result Sets are not required for your application, Result Set support can be disabled. There is a small performance penalty for procedures called from packages not containing Result Sets. Result Sets are enabled by default.
Enable Query Timeout - Enables query timeout for SQL queries. By default, the Oracle ODBC Driver supports the SQL_ATTR_QUERY_TIMEOUT attribute for the SQLSetStmtAttr function. If this box is not checked, the Oracle ODBC Driver responds with a 'not capable' message. Query Timeout is enabled by default.
Read-Only Connection - Check this box to force read-only access. The default is write access.
Enable Closing Cursors - Enables closing cursors. By default, closing cursors is disabled (the field is empty), meaning a call to close a cursor does not force the closing of OCI cursors when this behavior is not desired because it can cause an unnecessary performance hit. Enable closing cursors when you want to force the closing of OCI cursors upon a call to close a cursor.

Note:

There is an impact on performance each time a cursor is closed.

Enable Thread Safety - Thread safety can be disabled for a data source. If thread safety is not required, disabling this option eliminates the overhead of using thread safety. By default, thread safety is enabled.
Batch Autocommit Mode - By default, commit is executed only if all statements succeed.
Numeric Settings - Allows you to choose the numeric settings that determine the decimal and group separator characters when receiving and returning numeric data that is bound as strings. This option allows you to choose Oracle NLS settings (the default setting), Microsoft default regional settings (to provide a way to mirror the Oracle OLE DB driver's behavior for greater interoperability), or US numeric settings (which are necessary when using MS Access or DAO (Database Access Objects) in non-US environments).

The main configuration setup options are described in the Oracle ODBC Driver Configuration Dialog Box topic.

Oracle Options

Figure 21-5 is an example of the Oracle Options tab found on the Oracle ODBC Driver Configuration dialog box.

Figure 21-5 The Oracle Options Tab of the Oracle ODBC Driver Configuration Dialog Box

Description of 'Figure 21-5 The Oracle Options Tab of the Oracle ODBC Driver Configuration Dialog Box'

The following list is an explanation of the fields found on the Oracle Options tab shown in the preceding graphic:

Fetch Buffer Size - The amount of memory used to determine how many rows of data the ODBC Driver prefetches at a time from an Oracle database regardless of the number of rows the application program requests in a single query. However, the number of prefetched rows depends on the width and number of columns specified in a single query. Applications that typically fetch fewer than 20 rows of data at a time improve their response time, particularly over slow network connections or to heavily loaded servers. Setting Fetch Buffer Size too high can make response time worse or consume large amounts of memory.

Note:

When LONG and LOB data types are present, the number of rows prefetched by the ODBC Driver is not determined by the Fetch Buffer Size. The inclusion of the LONG and LOB data types minimizes the performance improvement and could result in excessive memory use. The ODBC Driver disregards Fetch Buffer Size and prefetches a set number of rows only in the presence of the LONG and LOB data types.

Enable LOBs - Enables the writing of Oracle LOBs. If writing Oracle LOBs is not required for your application, LOB support can be disabled. There is a small performance penalty for insert and update statements when LOBs are enabled. LOB writing is enabled by default but disabled for Oracle databases that do not support the LOB data type.
Enable Statement Caching - Enables statement caching feature, which increases the performance of parsing the query, in case the user has to parse the same text of query and related parameters multiple times. The default is disabled.
Cache Buffer Size - The statement cache has a maximum size (number of statements) that can be modified by an attribute on the service context, OCI_ATTR_STMTCACHESIZE. The default cache buffer size is 20 that are used only if statement caching option is enabled. Setting cache buffer size to 0 disables statement caching feature.
Max Token Size - Sets the token size to the nearest multiple of 1 KB (1024 bytes) beginning at 4 KB (4096 bytes). The default size is 8 KB (8192 bytes). The maximum value that can be set is 128 KB (131068 bytes).
Translate ORA errors - Any migrated third party ODBC application, which is using the SQL Translation Framework feature, expects that errors returned by the server to be in their native database format, then users can enable this option to receive native errors based on the error translation registered with SQL Translation Profile.
Convert Empty String - Any third party ODBC application that is migrated to Oracle Database requires handling empty string data (Oracle Database does not handle empty string data in table columns), then they can enable this option so that the application can insert empty string data or retrieve empty string data.
Note:
This feature is not implemented for Oracle Database 12c Release 1 (12.1.0.1).

The Failover area of the Oracle Options tab contains the following fields:

Enable Failover - Enables Oracle Fail Safe and Oracle Parallel Server failover retry. This option in an enhancement to the failover capabilities of Oracle Fail Safe and Oracle Parallel Server. Enable this option to configure additional failover retries. The default is enabled.
Retry - The number of times the connection failover is attempted. The default is 10 attempts.
Delay - The number of seconds to delay between failover attempts. The default is 10 seconds.

Note:

See the Oracle Fail Safe and Oracle Parallel Server documentation on how to set up and use both of these products.

The main configuration setup options are described in the Oracle ODBC Driver Configuration Dialog Box topic.

Workarounds Options

Figure 21-6 is an example of the Workarounds Options tab found on the Oracle ODBC Driver Configuration dialog box.

Figure 21-6 The Workarounds Options Tab of the Oracle ODBC Driver Configuration Dialog Box

Description of 'Figure 21-6 The Workarounds Options Tab of the Oracle ODBC Driver Configuration Dialog Box'

The following list is an explanation of the fields found on the Workarounds Options tab shown in the preceding graphic:

Bind TIMESTAMP as DATE - Check this box to force the Oracle ODBC Driver to bind SQL_TIMESTAMP parameters as the Oracle DATE type instead of as the Oracle TIMESTAMP type (the default). For more information, see Section 21.3.4, 'Implementation of Data Types (Advanced).'
Force SQL_WCHAR Support - Check this box to enable SQLDescribeCol, SQLColumns, and SQLProcedureColumns to unconditionally return the data type of SQL_WCHAR for SQL_CHAR columns; SQL_WVARCHAR for SQL_VARCHAR columns; and SQL_WLONGVARCHAR for SQL_LONGVARCHAR columns. This feature enables Unicode support in applications that rely on the results of these ODBC calls (for example, ADO). This support is disabled by default.
Disable Microsoft Transaction Server - Clear the check in this box to enable Microsoft Transaction Server (MTS) support. By default, MTS support is disabled.
Set Metadata Id Default to SQL_TRUE - Check this box to change the default value of the SQL_ATTR_METADATA_ID connection and statement attribute at connection time to SQL_TRUE. Under normal circumstances, SQL_ATTR_METADATA_ID would default to SQL_FALSE. ODBC calls made by the application to specifically change the value of the attribute after connection time are unaffected by this option and complete their functions as expected. By default, this option is off. The Implementation of ODBC API Functions topic provides additional information about the SQL_ATTR_METADATA_ID attribute.
Prefetch size for LONG column data - Set this value to prefetch LONG or LONG RAW data to improve performance of ODBC applications. This enhancement improves the performance of Oracle ODBC driver up to 10 times, depending on the prefetch size set by the user. The default value is 0. The maximum value that you can set is 64 KB (65536 bytes).
If the value of prefetch size is greater than 65536, the data fetched is only 65536 bytes. If you have LONG or LONG RAW data in the database that is greater that 65536 bytes, then set the prefetch size to 0 (the default value), which causes single-row fetch and fetches complete LONG data. If you pass a buffer size less than the prefetch size in nonpolling mode, a data truncation error occurs if the LONG data size in the database is greater than the buffer size.
Disable SQLDescribeParam - If the SQLDescribeParam function is enabled, the SQL_VARCHAR data type is returned for all parameters. If the Force SQL_WCHAR Support function is also enabled, the SQL_WVARCHAR data type is returned for all parameters. By default, this function is enabled.
Bind NUMBER as FLOAT - Check this box to force the Oracle ODBC Driver to bind NUMBER column containing FLOAT data as Float instead of as the Binary Float (the default).
Disable RULE Hint - Clear the check in this box to enable RULE Hint specified with catalogue queries. By default, RULE Hint option is disabled.
Use OCIDescribeAny - Check this box to gain a performance improvement by forcing the driver to use OCIDescribeAny()when an application makes heavy calls to small packaged procedures that return REF CURSORS.

The main configuration setup options are described in the Oracle ODBC Driver Configuration Dialog Box topic.

SQL Server Migration Options

Figure 21-7 is an example of the SQL Server Migration Options tab found on the Oracle ODBC Driver Configuration dialog box.

Figure 21-7 The SQL Server Migration Options Tab of the Oracle ODBC Driver Configuration Dialog Box

Description of 'Figure 21-7 The SQL Server Migration Options Tab of the Oracle ODBC Driver Configuration Dialog Box'

The fields of the SQL Server Migration Options tab in the preceding graphic are:

EXEC Syntax Enabled, which enables support for SQL Server EXEC syntax. A subprogram call specified in an EXEC statement is translated to its equivalent Oracle subprogram call before being processed by an Oracle database server. By default this option is disabled.
Schema, which is the translated Oracle subprogram assumed to be defined in the user's default schema. However, if all subprograms from the same SQL Server database are migrated to the same Oracle schema with their database name as the schema name, then set this field to database. If all subprograms owned by the same SQL Server user are defined in the same Oracle schema, then set this field to owner. This field is empty by default.

The main configuration setup options are described in the Oracle ODBC Driver Configuration Dialog Box topic.

21.2.3 Modifying the oraodbc.ini File

Topics:

21.2.3.1 Reducing Lock Timeout

An Oracle server waits indefinitely for lock conflicts between transactions to be resolved. You can limit the amount of time that an Oracle server waits for locks to be resolved by setting the Oracle ODBC Driver's LockTimeOut entry in the oraodbc.ini file. The value you enter for the LockTimeOut parameter is the number of seconds after which an Oracle server times out if it cannot obtain the requested locks. In the following example, the Oracle server times out after 60 seconds:

21.2.4 Connecting to a Data Source

Topics:

21.2.4.1 Connecting to an Oracle Data Source

To connect to a Data Source, the Oracle ODBC Driver requires that the OCI client software be installed on your computer and the corresponding listener be running on the Oracle server. Oracle Net Services for Windows is a Dynamic Linked Library (DLL) based application. For more information about Oracle Net Services, see the Oracle Net Services documentation.

As part of the connection process, an application can prompt you for information. If an application prompts you for information about an Oracle data source, do the following:

In the TNS Service Name box, enter the name of the TNS service.
In the User Name box, enter the name you use to access an Oracle Database.
In the Password box, enter the password you use to access an Oracle Database.
Click OK.

An application must connect to a data source to access the data in it. Different applications connect to data sources at different times. For example, an application might connect to a data source only at your request, or it might connect automatically when it starts. For information about when an application connects to a data source, see the documentation for that application.

For additional information, click any of these links.

21.2.5 Troubleshooting

Topics:

21.2.5.1 Using the Oracle ODBC Driver for the First Time

Note:

This information is only for Microsoft Windows users.

For the Oracle ODBC Driver to function successfully, OracleHome/bin must be in the system path. To verify this, type PATH from a command prompt.

The first time you use Oracle ODBC Driver and attempt to connect to a database or table, you might see these messages:

Your machine or server system is missing required software

Problem: Oracle ODBC Driver fails to work.
Cause: Either OCI software is not installed on your machine or Oracle database software is not installed on your server system.
Recommended Action: Install the required OCI software on your client machine or Oracle database software on your server system or both.

Client/Server connectivity is incorrectly set up on your machine

Problem: Cannot connect to the server system from your machine.
Cause: Either the required transport software is not installed or is not configured correctly.
Recommended Action: As a test, for example when using TCP/IP, make sure that your machine can ping to the server where the Oracle database resides. Use tnsping.exe located in the /orant/bin or /Oracle/ora90/bin directory to ensure connectivity to a specific database service. For example:
C:/ORANT/BIN>tnsping database-service-name

TNS Service Name does not match the name that was entered in the Oracle Net Configuration Assistant (NETCA)

Problem: The user is returned an error message about the TNS Service Name while attempting to set up the Oracle ODBC Driver.
Cause: The TNS Service Name does not match the name entered in NETCA.
Recommended Action: Change the TNS Service Name in the Oracle ODBC Driver setup window to match the TNS Service Name in NETCA.

Note:

Refer to the pull-down menu on the Datasource Configuration screen to view a list of all valid TNS service names on the system as well as names entered by users.

User does not have access to the database

Problem: The user is returned an access denied error message when attempting to gain access to an Oracle database while using the Oracle ODBC Driver.
Cause: You do not have access to an Oracle database.
Recommended Action: Ensure the proper privileges are assigned for the user to gain access to the Oracle database.

System Error: 182 or 193 when trying to create an ODBC DSN

Problem: You are trying to create a DSN with the ODBC Administrator but, after selecting the Oracle ODBC Driver, you received a System Error 182 or System Error 193.
Cause: This error is due to a mismatch in the mfc42.dll provided by Microsoft.
Recommended Action: Verified that OracleHome/bin is in your PATH and that you have no duplicate oci.dll outside the OracleHome/bin. If you still receive the error, copy the mfc42.dll from a working machine to the machine with the problem.

Translator Library could not be loaded system error code 31

Problem: On Windows with the Oracle ODBC Driver in the Microsoft ODBC Administrator trying to Add or Delete an Oracle ODBC DSN, you get the error 'Translator Library could not be loaded System error code 31.'
Cause: In some cases, a Windows machine contains an outdated version of the mfc42.dll. Oracle ODBC is built against the newer version of mfc42.dll (specifically, version 6.0.8665.0).
Recommended Action: An outdated version of the Microsoft DLL mfc42.dll is causing this error. Installing MDAC 2.5 SP1 does solve this problem. You must obtain a newer version of the mfc42.dll (version 6.0.8665.0 or higher) and replace the outdated mfc42.dll in the %WINNT%/System32 directory. Either copy the DLL from another machine that works correctly or contact Microsoft to find out how to obtain the DLL.

21.2.5.2 Expired Password

This section contains information about expired passwords.

Expired Password Behavior

If you try to connect to the database and your password has expired, you are prompted to change your password. Upon making a successful password change, you are connected to the database. However, if you try to connect to the database with a SQLDriverConnect call with a SQL_DRIVER_NOPROMPT parameter value, the Oracle ODBC Driver does not prompt you for the password change. Instead, an error condition results, producing an error message and number that indicates that the password has expired.

21.3 For Advanced Users

Topics:

21.3.1 Creating Oracle ODBC Driver TNS Service Names

To create Oracle ODBC Driver TNS Service Names with Oracle Net Services, use the Oracle Net Configuration Assistant (NETCA), which is installed when you install Oracle Net Services. NETCA creates Oracle ODBC Driver TNS Service Name entries in the tnsnames.ora file.

21.3.2 SQL Statements

The Oracle ODBC Driver is broadly compatible with the SQL-99 Core specification which is a superset of the SQL-92 Entry Level specification. In addition to Oracle's grammar, the vendor-specific escape sequences outlined in Appendix C of the ODBC specifications are also supported. In accordance with the design of ODBC, the Oracle ODBC Driver passes native SQL syntax to the Oracle database.

Related Topic for Programmers

21.3.3 Data Types

The Oracle ODBC Driver maps Oracle database data types to ODBC SQL data types.

Note:

All conversions in Appendix D of the Microsoft ODBC 3.52 Software Development Kit and Programmer's Reference are supported for the ODBC SQL data types listed from a call to SQLGetInfo with the appropriate information type.

Related Topic for Programmers

21.3.4 Implementation of Data Types (Advanced)

Topics:

DATE and TIMESTAMP

The semantics of Oracle DATE and TIMESTAMP data types do not correspond exactly with the ODBC data types with the same names. The Oracle DATE data type contains both date and time information while the SQL_DATE data type contains only date information. The Oracle TIMESTAMP data type also contains date and time information, but it has greater precision in fractional seconds. The ODBC Driver reports the data types of both Oracle DATE and TIMESTAMP columns as SQL_TIMESTAMP to prevent information loss. Similarly the ODBC Driver binds SQL_TIMESTAMP parameters as Oracle TIMESTAMP values.

Floating Point Data Types

When connected to a 10.1 or later Oracle server, the ODBC Driver maps the Oracle floating point data types BINARY_FLOAT and BINARY_DOUBLE to the ODBC data types SQL_REAL and SQL_DOUBLE, respectively. In previous releases, SQL_REAL and SQL_DOUBLE mapped to the generic Oracle numeric data type.

21.3.5 Limitations on Data Types

The Oracle ODBC Driver and the Oracle database impose limitations on data types. Table 21-3 describes these limitations.

Table 21-3 Limitations Imposed on Data Types by the Oracle ODBC Driver and Oracle Database

Limited Data Type	Description
Literals	Oracle database limits literals in SQL statements to 4,000 bytes.
SQL_LONGVARCHAR and SQL_WLONGVARCHAR	Oracle's limit for `SQL_LONGVARCHAR` data where the column type is `LONG` is 2,147,483,647 bytes. Oracle's limit for the `SQL_LONGVARCHAR` data where the column type is `CLOB` is 4 gigabytes. The limiting factor is the client workstation memory.
SQL_LONGVARCHAR and SQL_LONGVARBINARY	Oracle database allows only a single long data column per table. The long data types are `SQL_LONGVARCHAR` (`LONG`) and `SQL_LONGVARBINARY` (`LONG RAW`). Oracle recommends you use `CLOB` and `BLOB` columns instead. There is no restriction on the number of `CLOB` and `BLOB` columns in a table.

21.3.6 Error Messages

When an error occurs, the Oracle ODBC Driver returns the native error number, the SQLSTATE (an ODBC error code), and an error message. The driver derives this information both from errors detected by the driver and errors returned by the Oracle server.

Native Error

For errors that occur in the data source, the Oracle ODBC Driver returns the native error returned to it by the Oracle server. When the Oracle ODBC Driver or the Driver Manager detects an error, the Oracle ODBC Driver returns a native error of zero.

SQLSTATE

For errors that occur in the data source, the Oracle ODBC Driver maps the returned native error to the appropriate SQLSTATE. When the Oracle ODBC Driver detects an error, it generates the appropriate SQLSTATE. When the Driver Manager detects an error, it generates the appropriate SQLSTATE.

Error Message

For errors that occur in the data source, the Oracle ODBC Driver returns an error message based on the message returned by the Oracle server. For errors that occur in the Oracle ODBC Driver or the Driver Manager, the Oracle ODBC Driver returns an error message based on the text associated with the SQLSTATE.

Error messages have the following format:

The prefixes in brackets ( [ ] ) identify the source of the error. Table 21-4 shows the values of these prefixes returned by the Oracle ODBC Driver. When the error occurs in the data source, the [vendor] and [ODBC-component] prefixes identify the vendor and name of the ODBC component that received the error from the data source.

Table 21-4 Error Message Values of Prefixes Returned by the Oracle ODBC Driver

Error Source	Prefix	Value
Driver Manager	[vendor][ODBC-component][data-source]	[Microsoft/unixODBC][ODBC Driver Manager]N/A
Oracle ODBC Driver	[vendor][ODBC-component][data-source]	[ORACLE][ODBC Driver]N/A
Oracle server	[vendor][ODBC-component][data-source]	[ORACLE][ODBC Driver]N/A

For example, if the error message does not contain the [Ora] prefix shown in the following format, the error is an Oracle ODBC Driver error and should be self-explanatory.

If the error message contains the [Ora] prefix shown in the following format, it is not an Oracle ODBC Driver error.

Note:

Although the error message contains the [Ora] prefix, the actual error may be coming from one of several sources.

If the error message text starts with the following prefix, you can obtain more information about the error in the Oracle server documentation.

Oracle Net Services errors and Trace logging are located under the ORACLE_HOMENETWORK directory on Windows systems or the ORACLE_HOME/NETWORK directory on UNIX systems where the OCI software is installed and specifically in the log and trace directories respectively. Database logging is located under the ORACLE_HOMERDBMS directory on Windows systems or the ORACLE_HOME/rdbms directory on UNIX systems where the Oracle server software is installed.

See the Oracle server documentation for more information about server error messages.

21.4 For Programmers

Topics:

21.4.1 Format of the Connection String

Table 21-5 describes keywords that can be included in the connection string argument of the SQLDriverConnect function call. Missing keywords are read from the Administrator entry for the data source. Values specified in the connection string override those contained in the Administrator entry. See the Microsoft ODBC 3.52 Software Development Kit and Programmer's Reference for more information about the SQLDriverConnect function.

Table 21-5 Keywords that Can Be Included in the Connection String Argument of the SQLDriverConnect Function Call

Keyword	Meaning	Comments
DSN	ODBC Data Source Name	User-supplied name.
DBQ	TNS Service Name	User-supplied name.
UID	User ID or User Name	User-supplied name.
PWD	Password	User-supplied password. Specify PWD=; for an empty password.
DBA	Database Attribute	W=write access. R=read-only access.
APA	Applications Attributes	T=Thread Safety Enabled. F=Thread Safety Disabled.
RST	Result Sets	T=Result Sets Enabled. F=Result Sets Disabled.
QTO	Query Timeout Option	T=Query Timeout Enabled. F=Query Timeout Disabled.
CSR	Close Cursor	T=Close Cursor Enabled. F=Close Cursor Disabled.
BNF	Bind `NUMBER` as `FLOAT`	T=Bind `NUMBER` as `FLOAT`. F=Bind `NUMBER` as `NUMBER`.
DRH	Disable Rule Hint	T=Disable Rule Hint. F=Enable Rule Hint.
BAM	Batch Autocommit Mode	IfAllSuccessful=Commit only if all statements are successful (old behavior). UpToFirstFailure=Commit up to first failing statement (V7 ODBC behavior). AllSuccessful=Commit all successful statements (only when connected to an Oracle database; against other databases, same behavior as V7).
FBS	Fetch Buffer Size	User-supplied numeric value (specify a value in bytes of 0 or greater). The default is 60,000 bytes.
FEN	Failover	T=Failover Enabled. F=Failover Disabled.
FRC	Failover Retry Count	User-supplied numeric value. The default is 10.
FDL	Failover Delay	User-supplied numeric value. The default is 10.
LOB	LOB Writes	T=LOBs Enabled. F=LOBs Disabled.
MTS	Microsoft Transaction Server Support	T=Disabled. F=Enabled.
FWC	Force `SQL_WCHAR` Support	T=Force `SQL_WCHAR` Enabled. F=Force `SQL_WCHAR` Disabled.
EXC	EXEC Syntax	T=EXEC Syntax Enabled. F=EXEC Syntax Disabled.
XSM	Schema Field	Default=Default. Database=Database Name. Owner=Owner Name.
MDI	Set Metadata ID Default	T=`SQL_ATTR_METADATA_ID` defaults to `SQL_TRUE`. F=`SQL_ATTR_METADATA_ID` defaults to `SQL_FALSE`.
DPM	Disable `SQLDescribeParam`	T=`SQLDescribeParam` Disabled. F=`SQLDescribeParam` Enabled.
BTD	Bind `TIMESTAMP` as `DATE`	T=Bind `SQL_TIMESTAMP` as Oracle `DATE` F=Bind `SQL_TIMESTAMP` as Oracle `TIMESTAMP`
NUM	Numeric Settings	NLS=Use Oracle NLS numeric settings (to determine the decimal and group separator). MS=Use Microsoft regional settings. US=Use US settings.
ODA	Use `OCIDescribeAny( )`	T= Use `OCIDescribeAny()` call to gain performance improvement when application makes heavy calls to small packaged procedures that return `REF CURSORS`. F= Do not use `OCIDescribeAny()`. By default, use `OCIDescribeAny()` value is `FALSE`.
STE	SQL Translate ORA Errors Specifies whether the Oracle ODBC Driver is to translate the Oracle error codes	T=Translate ORA errors. F=Do not translate any ORA error. By default, `SQLTranslateErrors` is `FALSE`.
TSZ	Token Size	User-supplied numeric value. Sets the token size to the nearest multiple of 1 KB (1024 bytes) beginning at 4 KB (4096 bytes). The default size is 8 KB (8192 bytes). The maximum value that can be set is 128 KB (131068 bytes).

If the following keyword is specified in the connection string, the Oracle ODBC Driver does not read values defined from the Administrator:

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Examples of valid connection strings are:

For additional information, click any of these links.

Related Topic for Programmers

21.4.2 SQLDriverConnect Implementation

Table 21-6 describes the keywords required by the SQLDriverConnect connection string.

Table 21-6 Keywords Required by the SQLDriverConnect Connection String

Keyword	Description
DSN	The name of the data source.
DBQ	The TNS Service Name. See Section 21.3.1, 'Creating Oracle ODBC Driver TNS Service Names.' For more information, see the Oracle Net Services documentation.
UID	The user login ID or user name.
PWD	The user-specified password.

21.4.3 Reducing Lock Timeout in a Program

The Oracle server waits indefinitely for lock conflicts between transactions to be resolved. You can limit the amount of time that the Oracle server waits for locks to be resolved by calling the ODBC SQLSetConnectAttr function before connecting to the data source. Specify a nonzero value for the SQL_ATTR_QUERY_TIMEOUT attribute in the ODBC SQLSetStmtAttr function.

If you specify a lock timeout value using the ODBC SQLSetConnectAttr function, it overrides any value specified in the oraodbc.ini file. Refer to Reducing Lock Timeout for more information on specifying a value in the oraodbc.ini file.

21.4.4 Linking with odbc32.lib (Windows) or libodbc.so (UNIX)

For Windows platforms, when you link your program, you must link it with the import library odbc32.lib.

For UNIX platforms, an ODBC application must be linked to libodbc.so.

21.4.5 Obtaining Information About rowids

The ODBC SQLSpecialColumns function returns information about the columns in a table. When used with the Oracle ODBC Driver, it returns information about the Oracle rowids associated with an Oracle table.

21.4.6 Rowids in a WHERE Clause

Rowids can be used in the WHERE clause of an SQL statement. However, the rowid value must be presented in a parameter marker.

21.4.7 Enabling Result Sets

Oracle reference cursors (Result Sets) allow an application to retrieve data using stored procedures and stored functions. The following information identifies how to use reference cursors to enable Result Sets through ODBC.

The ODBC syntax for calling stored procedures must be used. Native PL/SQL is not supported through ODBC. The following identifies how to call the procedure or function without a package and within a package. The package name in this case is RSET.
The PL/SQL reference cursor parameters are omitted when calling the procedure. For example, assume procedure Example2 is defined to have four parameters. Parameters 1 and 3 are reference cursor parameters and parameters 2 and 4 are character strings. The call is specified as:

The following example application shows how to return a Result Set using the Oracle ODBC Driver:

21.4.8 Enabling EXEC Syntax

If the syntax of your SQL Server EXEC statement can be readily translated to an equivalent Oracle procedure call without change, the Oracle ODBC Driver can translate it if you enable this option.

The complete name of a SQL Server procedure consists of up to four identifiers:

server name
database name
owner name
procedure name

The format for the name is:

During the migration of the SQL Server database to Oracle, the definition of each SQL Server procedure (or function) is converted to its equivalent Oracle syntax and is defined in a schema in Oracle. Migrated procedures are often reorganized (and created in schemas) in one of these ways:

All procedures are migrated to one schema (the default option).
All procedures defined in one SQL Server database are migrated to the schema named with that database name.
All procedures owned by one user are migrated to the schema named with that user's name.

To support these three ways of organizing migrated procedures, you can specify one of these schema name options for translating procedure names. Object names in the translated Oracle procedure call are not case-sensitive.

21.4.9 Enabling Event Notification for Connection Failures in an Oracle RAC Environment

If the SQL_ORCLATTR_FAILOVER_CALLBACK and SQL_ORCLATTR_FAILOVER_HANDLE attributes of the SQLSetConnectAttr function are set when a connection failure occurs in an Oracle Real Application Clusters (Oracle RAC) Database environment, event notification is enabled. Both attributes are set using the SQLSetConnectAttr function. The symbols for the new attributes are defined in the file sqora.h.

The SQL_ORCLATTR_FAILOVER_CALLBACK attribute specifies the address of a routine to call when a failure event takes place.

The SQL_ORCLATTR_FAILOVER_HANDLE attribute specifies a context handle that is passed as a parameter in the callback routine. This attribute is necessary for the ODBC application to determine which connection the failure event is taking place on.

The function prototype for the callback routine is:

The 'handle' parameter is the value that was set by the SQL_ORCLATTR_FAILOVER_HANDLE attribute. Null is returned if the attribute has not been set.

The fo_code parameter identifies the failure event which is taking place. The failure events map directly to the events defined in the OCI programming interface. The list of possible events is:

ODBC_FO_BEGIN
ODBC_FO_ERROR
ODBC_FO_ABORT
ODBC_FO_REAUTH
ODBC_FO_END

The following is a sample program which demonstrates using this feature:

21.4.10 Using Implicit Results Feature Through ODBC

Use this option when you migrate any third party ODBC application to Oracle Database and you want to use implicit results functionality as supported by the previous vendor. Oracle ODBC driver supports implicit results with stored procedures or an anonymous PL/SQL block. For the current release, implicit results are returned only for SELECT statements.

The following code example shows an example ODBC test case using an anonymous SQL script for implicit results.

21.4.11 Supported Functionality

Topics:

21.4.11.1 API Conformance

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Oracle ODBC Driver release 9.2.0.0.0 and higher supports all Core, Level 2, and Level 1 functions.

Also, Oracle ODBC Driver release 9.2.0.0.0 and higher supports translation DLLs.

The following topics describe the ODBC API functions implemented by the Oracle ODBC Driver.

Related Topic for Programmers

21.4.11.2 Implementation of ODBC API Functions

Table 21-7 describes how the Oracle ODBC Driver implements specific functions:

Table 21-7 How Oracle ODBC Driver Implements Specific Functions

Function	Description
`SQLConnect`	SQLConnect requires only a DBQ, user ID, and password.
`SQLDriverConnect`	SQLDriverConnect uses the DSN, DBQ, UID, and PWD keywords.
`SQLMoreResults`	Implements ODBC support for implicit results. This is a new API implemented for Oracle Database 12c Release 1 (12.1.0.1). See `http://msdn.microsoft.com/en-us/library/ms714673(v=VS.85).aspx` for more information.
`SQLSpecialColumns`	If `SQLSpecialColumns` is called with the `SQL_BEST_ROWID` attribute, it returns the rowid column.
`SQLProcedures` and`SQLProcedureColumns`	See the information that follows.
All catalog functions	If the `SQL_ATTR_METADATA_ID` statement attribute is `SQL_TRUE`, a string argument is treated as an identifier argument, and its case is not significant. In this case, the underscore ('_') and the percent sign ('%') are treated as the actual character, not as a search pattern character. On the other hand, if this attribute is `SQL_FALSE`, it is either an ordinary argument or a pattern value argument and is treated literally, and its case is significant.

21.4.11.3 Implementation of the ODBC SQL Syntax

If a comparison predicate has a parameter marker as the second expression in the comparison and the value of that parameter is SQL_NULL_DATA with SQLBindParameter, the comparison fails. This is consistent with the null predicate syntax in ODBC SQL.

21.4.11.4 Implementation of Data Types (Programming)

For programmers, the noteworthy part of the implementation of the data types concerns the CHAR, VARCHAR, and VARCHAR2 data types.

For an fSqlType value of SQL_VARCHAR, SQLGetTypeInfo returns the Oracle database data type VARCHAR2. For an fSqlType value of SQL_CHAR, SQLGetTypeInfo returns the Oracle database data type CHAR.

21.4.12 Unicode Support

Topics:

21.4.12.1 Unicode Support Within the ODBC Environment

The Microsoft or unixODBC ODBC Driver Manager (Driver Manager) makes all ODBC drivers, regardless if they support Unicode, appear as if they are Unicode compliant. This allows ODBC applications to be written independent of the Unicode capabilities of underlying ODBC drivers.

The extent to which the Driver Manager can emulate Unicode support for ANSI ODBC drivers is limited by the conversions possible between the Unicode data and the local code page. Data loss is possible when the Driver Manager is converting from Unicode to the local code page. Full Unicode support is not possible unless the underlying ODBC driver supports Unicode. The Oracle ODBC Driver provides full Unicode support.

21.4.12.2 Unicode Support in ODBC API

The ODBC API supports both Unicode and ANSI entry points using the 'W' and 'A' suffix convention. An ODBC application developer need not explicitly call entry points with the suffix. An ODBC application that is compiled with the UNICODE and _UNICODE preprocessor definitions generates the appropriate calls. For example, a call to SQLPrepare is compiled as SQLPrepareW.

The C data type, SQL_C_WCHAR, was added to the ODBC interface to allow applications to specify that an input parameter is encoded as Unicode or to request column data returned as Unicode. The macro SQL_C_TCHAR is useful for applications that must be built as both Unicode and ANSI. The SQL_C_TCHAR macro compiles as SQL_C_WCHAR for Unicode applications and as SQL_C_CHAR for ANSI applications.

The SQL data types, SQL_WCHAR, SQL_WVARCHAR, and SQL_WLONGVARCHAR, have been added to the ODBC interface to represent columns defined in a table as Unicode. Potentially, these values are returned from calls to SQLDescribeCol, SQLColAttribute, SQLColumns, and SQLProcedureColumns.

Unicode encoding is supported for SQL column types NCHAR, NVARCHAR2, and NCLOB. Also, Unicode encoding is also supported for SQL column types CHAR and VARCHAR2 if the character semantics are specified in the column definition.

The ODBC Driver supports these SQL column types and maps them to ODBC SQL data types.

Table 21-8 lists the supported SQL data types and the equivalent ODBC SQL data type.

Table 21-8 Supported SQL Data Types and the Equivalent ODBC SQL Data Type

SQL Data Types	ODBC SQL Data Types
`CHAR`	`SQL_CHAR` or `SQL_WCHAR`^{Foot 1}
`VARCHAR2`	`SQL_VARCHAR` or `SQL_WVARCHAR`^{Foot 2}
`NCHAR`	`SQL_WCHAR`
`NVARCHAR2`	`SQL_WVARCHAR`
`NCLOB`	`SQL_WLONGVARCHAR`

^{Footnote 1}CHAR maps to SQL_WCHAR if the character semantics were specified in the column definition and if the character set for the database is Unicode.

^{Footnote 2}VARCHAR2 maps to SQL_WVARCHAR if the character semantics were specified in the column definition and if the character set for the database is Unicode.

21.4.12.3 Unicode Functions in the Driver Manager

The Driver Manager performs the following functions when it detects that the underlying ODBC driver does not support Unicode:

Convert Unicode function calls to ANSI function calls before calling the ANSI ODBC driver. String arguments are converted from Unicode to the local code page. For example, a call to SQLPrepareW is converted to call SQLPrepare. The text of the SQL statement parameter is converted from Unicode to the local code page.
Convert return parameters that are character data from the local code page to Unicode. For example, returning the column name through SQLColAttribute.
Convert data from the local code page to Unicode for columns bound as SQL_C_WCHAR.
Convert data from Unicode to the local code page for input parameters bound as SQL_C_WCHAR.

21.4.12.4 SQLGetData Performance

The SQLGetData function allows an ODBC application to specify the data type to receive a column as after the data has been fetched. OCI requires the Oracle ODBC Driver to specify the data type before it is fetched. In this case, the Oracle ODBC Driver uses the knowledge it has about the data type of the column as defined in the database to determine how to best default to fetching the column through OCI.

If a column that contains character data is not bound by SQLBindCol, the Oracle ODBC Driver must determine if it must fetch the column as Unicode or as the local code page. The driver could default to receiving the column as Unicode, however, this may result in as many as two unnecessary conversions. For example, if the data were encoded in the database as ANSI, there would be an ANSI to Unicode conversion to fetch the data into the Oracle ODBC Driver. If the ODBC application then requested the data as SQL_C_CHAR, there would be an additional conversion to revert the data back to its original encoding.

The default encoding of the Oracle client is used when fetching data. However, an ODBC application can overwrite this default and fetch the data as Unicode by binding the column or the parameter as the WCHAR data type.

21.4.12.5 Unicode Samples

As the Oracle ODBC Driver itself was implemented using TCHAR macros, Oracle recommends that ODBC application programs use TCHAR to take advantage of the driver.

The following links are program examples showing how to use TCHAR, which becomes the WCHAR data type in case you compile with UNICODE and _UNICODE.

Example 1: Connection to Database

No difference other than specifying Unicode literals for SQLConnect.

Example 2: Simple Retrieval

The following example retrieves the employee names and the job titles from the EMP table. With the exception that you must specify TCHAR compliant data to every ODBC function, there is no difference to the ANSI case. If the case is a Unicode application, you have to specify the length of the buffer to the BYTE length when you call SQLBindCol (for example, sizeof(ename) ).

Example 3: Retrieval Using SQLGetData (Binding After Fetch)

This example shows how to use SQLGetData. For those who are not familiar with ODBC programming, the fetch is allowed before binding the data using SQLGetData, unlike in an OCI program. There is no difference to the ANSI application in terms of Unicode-specific issues.

Example 4: Simple Update

This example shows how to update data. Likewise, the length of data for SQLBindParameter has to be specified with the BYTE length, even in the case of a Unicode application.

Example 5: Update and Retrieval for Long Data (CLOB)

This example may be the most complicated case to update and retrieve data for long data, like CLOB, in Oracle. Because the length of data must be the BYTE length, lstrlen(TCHAR data)*sizeof(TCHAR) is needed to derive the BYTE length.

21.4.13 Performance and Tuning

Topics:

21.4.13.1 General ODBC Programming Tips

This section describes some general programming tips to improve the performance of an ODBC application.

Enable connection pooling if the application will frequently connect and disconnect from a data source. Reusing pooled connections is extremely efficient compared to reestablishing a connection.
Minimize the number of times a statement must be prepared. Where possible, use bind parameters to make a statement reusable for different parameter values. Preparing a statement once and executing it several times is much more efficient than preparing the statement for every SQLExecute.
Do not include columns in a SELECT statement if you know the application will not retrieve them; especially LONG columns. Due to the nature of the database server protocols, the ODBC Driver must fetch the entire contents of a LONG column if it is included in the SELECT statement, regardless if the application binds the column or does a SQLGetData.
If you are performing transactions that do not update the data source, set the SQL_ATTR_ACCESS_MODE attribute of the ODBC SQLSetConnectAttr function to SQL_MODE_READ_ONLY.
If you are not using ODBC escape clauses, set the SQL_ATTR_NOSCAN attribute of the ODBC SQLSetConnectAttr function or the ODBC SQLSetStmtAttr function to true.
Use the ODBC SQLFetchScroll function instead of the ODBC SQLFetch function for retrieving data from tables that have a large number of rows.
Enable OCI statement caching when the same SQL statements are used multiple times (StatementCache=T).
Binding NUMBER columns as FLOAT speeds up query execution (BindAsFLOAT=T).
While fetching LONG or LONG RAW set MaxLargeData=<value> for optimum performance.
Setting UseOCIDescribeAny=T for applications making heavy calls to small packaged procedures that return Ref Cursor improves performance.

21.4.13.2 Data Source Configuration Options

This topic discusses performance implications of the following ODBC data source configuration options:

Topics:

Enable Result Sets

This option enables the support of returning result sets (for example, RefCursor) from procedure calls. The default is enabling the returning of result sets.

The ODBC Driver must query the database server to determine the set of parameters for a procedure and their data types to determine if there are any RefCursor parameters. This query incurs an additional network round trip the first time any procedure is prepared and executed.

Enable LOBs

This option enables the support of inserting and updating LOBs. The default is enabled.

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The ODBC Driver must query the database server to determine the data types of each parameter in an INSERT or UPDATE statement to determine if there are any LOB parameters. This query incurs an additional network round trip the first time any INSERT or UPDATE is prepared and executed.

Bind TIMESTAMP as DATE

Binds SQL_TIMESTAMP parameters as the appropriate Oracle data type. If this option is TRUE, SQL_TIMESTAMP binds as the Oracle DATE data type. If this option is FALSE, SQL_TIMESTAMP binds as the Oracle TIMESTAMP data type (which is the default).

Enable Closing Cursors

The SQL_CLOSE option of the ODBC function, SQLFreeStmt, is supposed to close associated cursors with a statement and discard all pending results. The application can reopen the cursor by executing the statement again without doing a SQLPrepare again. A typical scenario for this is an application that is idle for a while but reuses the same SQL statement. While the application is idle, it might free up associated server resources.

The Oracle Call Interface (OCI), on which the Oracle ODBC Driver is layered, does not support the functionality of closing cursors. So, by default, the SQL_CLOSE option has no effect in the Oracle ODBC Driver. The cursor and associated resources remain open on the database server.

Enabling this option causes the associated cursor to be closed on the database server. However, this results in the parse context of the SQL statement being lost. The ODBC application can execute the statement again without calling SQLPrepare. However, internally the ODBC Driver must prepare and execute the statement all over. Enabling this option severely impacts performance of applications that prepare a statement once and execute it repeatedly.

Enable this option only if freeing the resources on the server is absolutely necessary.

Enable Thread Safety

If an application is single-threaded, this option can be disabled. By default, the ODBC Driver ensures that access to all internal structures (environment, connection, statement) are thread-safe. Single-threaded applications can eliminate some of the thread safety overhead by disabling this option. Disabling this option typically shows a minor performance improvement.

Fetch Buffer Size

Set the Fetch Buffer Size in the Oracle Options tab of the Oracle ODBC Driver Configuration Dialog Box to a value specified in bytes. This value determines how many rows of data at a time the ODBC Driver prefetches from an Oracle database to the client's cache, regardless of the number of rows the application program requests in a single query, thus improving performance.

Applications that typically fetch fewer than 20 rows of data at a time improve their response time, particularly over slow network connections or to heavily loaded servers. Setting this too high can worsen response time or consume large amounts of memory. The default is 64,000 bytes. Choose a value that works best for your application.

Note:

When LONG and LOB data types are present, the number of rows prefetched by the ODBC Driver is not determined by the Fetch Buffer Size. The inclusion of the LONG and LOB data types minimizes the performance improvement and could result in excessive memory use. The ODBC Driver disregards the Fetch Buffer Size and prefetch a set number of rows in the presence of the LONG and LOB data types.

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21.4.13.3 DATE and TIMESTAMP Data Types

If a DATE column in the database is used in a WHERE clause and the column has an index, there can be an impact on performance. For example:

In this example, an index on the HIREDATE column could be used to make the query execute quickly. But, because HIREDATE is actually a DATE value and the ODBC Driver is supplying the parameter value as TIMESTAMP, the Oracle server's query optimizer must apply a conversion function. To prevent incorrect results (as might happen if the parameter value had nonzero fractional seconds), the optimizer applies the conversion to the HIREDATE column resulting in the following statement:

Unfortunately, this has the effect of disabling the use of the index on the HIREDATE column and instead the server performs a sequential scan of the table. If the table has many rows, this can take a long time. As a workaround for this situation, the ODBC Driver has the connection option to Bind TIMESTAMP as DATE. When this option is enabled, the ODBC Driver binds SQL_TIMESTAMP parameters as the Oracle DATE data type instead of the Oracle TIMESTAMP data type. This allows the query optimizer to use any index on the DATE columns.

Note:

This option is intended for use only with Microsoft Access or other similar programs that bind DATE columns as TIMESTAMP columns. Do not use this option when there are actual TIMESTAMP columns present or when data loss may occur. Microsoft Access executes such queries using whatever columns are selected as the primary key.