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11g Release 1 (11.1) for Linux and UNIX-Based Operating Systems

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E Using Oracle ODBC Driver

Note:

Oracle ODBC Driver is supported only on the Linux x86 and Oracle Solaris on SPARC platforms.

This appendix provides information related to using Oracle ODBC Driver. It contains the following sections:

E.1 Features Not Supported

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

Oracle ODBC Driver does not support the SQL functions listed in the following table:

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

 

E.2 Implementation of Data Types

This section discusses the DATE, TIMESTAMP, and floating point data types.

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. 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. Oracle ODBC Driver reports the data types of both Oracle DATE and TIMESTAMP columns as SQL_TIMESTAMP to prevent information loss. Similarly, Oracle ODBC Driver binds SQL_TIMESTAMP parameters as Oracle TIMESTAMP values.

See Also:

"DATE and TIMESTAMP Data Types" for information about the DATE and TIMESTAMP data types related to performance and tuning

Floating Point Data Types

When connected to a release 11.1 or later Oracle Database, Oracle 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 earlier releases, SQL_REAL and SQL_DOUBLE mapped to the generic Oracle numeric data type.

E.3 Limitations on Data Types

Oracle ODBC Driver and Oracle Database impose limitations on data types. The following table describes these limitations:

Limited Data Type Description
Literals Oracle Database limits literals in SQL statements to 4000 bytes.
SQL_LONGVARCHAR and SQL_WLONGVARCHAR The Oracle limit for SQL_LONGVARCHAR data, where the column type is LONG, is 2,147,483,647 bytes. The Oracle limit for 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 permits only a single long data column in each table. The long data types are SQL_LONGVARCHAR (LONG) and SQL_LONGVARBINARY (LONG RAW). Oracle recommends that you use CLOB and BLOB columns instead. There is no restriction on the number of CLOB and BLOB columns in a table.

E.4 Format of the Connection String for the SQLDriverConnect Function

The SQLDriverConnect function is one of the functions implemented by Oracle ODBC Driver. The following table describes the keywords that you can include in the connection string argument of the SQLDriverConnect function call:

Keyword Meaning Value
DSN ODBC data source name User-supplied name

This is a mandatory keyword.

DBQ TNS service name User-supplied name

This is a mandatory keyword.

UID User ID or user name User-supplied name

This is a mandatory keyword.

PWD Password User-supplied name

Specify PWD=; for an empty password.

This is a mandatory keyword.

DBA Database attribute W implies write access

R implies read-only access

APA Applications attributes T implies that thread safety is to be enabled

F implies that thread safety is to be disabled

RST Result sets T implies that result sets are to be enabled.

F implies that result sets are to be disabled.

QTO Query timeout option T implies that query timeout is to be enabled.

F implies that query timeout is to be disabled.

CSR Close cursor T implies that close cursor is to be enabled.

F implies that close cursor is to be disabled.

BAM Batch autocommit mode IfAllSuccessful implies commit only if all statements are successful (old behavior).

UpToFirstFailure implies commit up to first failing statement. This is ODBC version 7 behavior.

AllSuccessful implies commit all successful statements.

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 implies failover is to be enabled.

F implies failover is to be 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 implies LOBs are to be enabled.

F implies LOBs are to be disabled.

FWC Force SQL_WCHAR support T implies Force SQL_WCHAR is to be enabled.

F implies Force SQL_WCHAR is to be disabled.

EXC EXEC syntax T implies EXEC Syntax is to be enabled.

F implies EXEC Syntax is to be disabled.

XSM Schema field Default implies that the default value is to be used.

Database implies that the Database Name is to be used.

Owner implies that the name of the owner is to be used.

MDI Set metadata ID default T implies that the default value of SQL_ATTR_METADATA_ID is SQL_TRUE.

F implies that the default value of SQL_ATTR_METADATA_ID is SQL_FALSE.

DPM Disable SQLDescribeParam T implies that SQLDescribeParam is to be disabled.

F implies that SQLDescribeParam is to be enabled.

BTD Bind TIMESTAMP as DATE T implies that SQL_TIMESTAMP is to be bound as Oracle DATE.

F implies that SQL_TIMESTAMP is to be bound as Oracle TIMESTAMP.

NUM Numeric settings NLS implies that the Globalization Support numeric settings are to be used (to determine the decimal and group separator).

E.5 Reducing Lock Timeout in a Program

Oracle Database waits indefinitely for lock conflicts between transactions to be resolved. However, you can limit the amount of time that Oracle Database waits for locks to be resolved. To do this, set the SQL_ATTR_QUERY_TIMEOUT attribute of the ODBC SQLSetStmtAttr function while calling this function before connecting to the data source.

E.6 Linking ODBC Applications

When you link the program, you must link it with the Driver Manager library, libodbc.so.

E.7 Obtaining Information About ROWIDs

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

E.8 ROWIDs in a WHERE Clause

ROWIDs may be used in the WHERE clause of an SQL statement. However, the ROWID value must be presented in a parameter marker.

E.9 Enabling Result Sets

Oracle reference cursors, also known as result sets, enable an application to retrieve data using stored procedures and stored functions. The following information describes how to use reference cursors to enable result sets through ODBC:

The following sample application shows how to return a result set by using Oracle ODBC Driver:

/*
* Sample Application using Oracle reference cursors through ODBC
*
* Assumptions:
*
* 1) Oracle Sample database is present with data loaded for the EMP table.
*
* 2) Two fields are referenced from the EMP table, ename and mgr.
*
* 3) A data source has been setup to access the sample database.
*
*
* Program Description:
*
* Abstract:
*
* This program demonstrates how to return result sets using
* Oracle stored procedures
*
* Details:
*
* This program:
* Creates an ODBC connection to the database.
* Creates a Packaged Procedure containing two result sets.
* Executes the procedure and retrieves the data from both result sets.
* Displays the data to the user.
* Deletes the package then logs the user out of the database.
*
*
* The following is the actual PL/SQL this code generates to
* create the stored procedures.
*  
DROP PACKAGE   ODBCRefCur;
CREATE PACKAGE ODBCRefCur AS
     TYPE ename_cur IS REF CURSOR;
     TYPE mgr_cur   IS REF CURSOR;
PROCEDURE EmpCurs(Ename IN OUT ename_cur, Mgr IN OUT mgr_cur, pjob IN VARCHAR2); 

END; 

/
CREATE PACKAGE BODY ODBCRefCur AS
PROCEDURE EmpCurs(Ename IN OUT ename_cur, Mgr IN OUT mgr_cur, pjob IN VARCHAR2)
     AS
       BEGIN
          IF NOT Ename%ISOPEN
          THEN
              OPEN Ename for SELECT ename from emp;
          END IF; 

          IF NOT Mgr%ISOPEN
          THEN
              OPEN Mgr for SELECT mgr from emp where job = pjob;
          END IF;
       END;
END;
/ 


*
*  End PL/SQL for Reference Cursor. 
*/

/*
 * Include Files
 */
#include <stdio.h>
#include <sql.h>
#include <sqlext.h>
/*
 * Defines
 */
#define JOB_LEN 9
#define DATA_LEN 100
#define SQL_STMT_LEN 500
/*
 * Procedures
 */
void DisplayError( SWORD HandleType, SQLHANDLE hHandle, char *Module );
/*
 * Main Program
 */
int main()
{
SQLHENV hEnv;
SQLHDBC hDbc;
SQLHSTMT hStmt;
SQLRETURN rc;
char *DefUserName ="jones";
char *DefPassWord ="password";
SQLCHAR ServerName[DATA_LEN];
SQLCHAR *pServerName=ServerName;
SQLCHAR UserName[DATA_LEN];
SQLCHAR *pUserName=UserName;
SQLCHAR PassWord[DATA_LEN];
SQLCHAR *pPassWord=PassWord;
char Data[DATA_LEN];
SQLINTEGER DataLen;
char error[DATA_LEN];
char *charptr;
SQLCHAR SqlStmt[SQL_STMT_LEN];
SQLCHAR *pSqlStmt=SqlStmt;
char *pSalesMan = "SALESMAN";
SQLINTEGER sqlnts=SQL_NTS;
/*
 * Allocate the Environment Handle
 */
rc = SQLAllocHandle( SQL_HANDLE_ENV, SQL_NULL_HANDLE, &hEnv );
if (rc != SQL_SUCCESS)
{
  printf( "Cannot Allocate Environment Handle\n");
  printf( "\nHit Return to Exit\n");
  charptr = gets ((char *)error);
  exit(1);
}
/*
 * Set the ODBC Version
 */
rc = SQLSetEnvAttr( hEnv,SQL_ATTR_ODBC_VERSION,(void *)SQL_OV_ODBC3,0);
if (rc != SQL_SUCCESS)
{
  printf( "Cannot Set ODBC Version\n");
  printf( "\nHit Return to Exit\n");
  charptr = gets ((char *)error);
  exit(1);
}
/*
 * Allocate the Connection handle
 */
rc = SQLAllocHandle( SQL_HANDLE_DBC, hEnv, &hDbc );
if (rc != SQL_SUCCESS)
{
  printf( "Cannot Allocate Connection Handle\n");
  printf( "\nHit Return to Exit\n");
  charptr = gets ((char *)error);
  exit(1);
}
/*
 * Get User Information
 */
strcpy ((char *) pUserName, DefUserName );
strcpy ((char *) pPassWord, DefPassWord );
/*
 * Data Source name
 */
printf( "\nEnter the ODBC Data Source Name\n" );
charptr = gets ((char *) ServerName);
/*
 * User Name
 */
printf ( "\nEnter User Name Default [%s]\n", pUserName);
charptr = gets ((char *) UserName);
if (*charptr == '\0')
{
  strcpy ((char *) pUserName, (char *) DefUserName );
}
/*
 * Password
 */
printf ( "\nEnter Password Default [%s]\n", pPassWord);
charptr = gets ((char *)PassWord);
if (*charptr == '\0')
{
  strcpy ((char *) pPassWord, (char *) DefPassWord );
}
/*
 * Connection to the database
 */
rc = SQLConnect( hDbc,pServerName,(SQLSMALLINT) strlen((char  *)pServerName),pUserName,(SQLSMALLINT) strlen((char *)pUserName),pPassWord,(SQLSMALLINT) strlen((char *)pPassWord));
if (rc != SQL_SUCCESS)
{
  DisplayError(SQL_HANDLE_DBC, hDbc, "SQLConnect");
}
/*
 * Allocate a Statement
 */
rc = SQLAllocHandle( SQL_HANDLE_STMT, hDbc, &hStmt );
if (rc != SQL_SUCCESS)
{
  printf( "Cannot Allocate Statement Handle\n");
  printf( "\nHit Return to Exit\n");
  charptr = gets ((char *)error);
  exit(1);
}
/*
 * Drop the Package
 */
strcpy( (char *) pSqlStmt, "DROP PACKAGE ODBCRefCur");
rc = SQLExecDirect(hStmt, pSqlStmt, strlen((char *)pSqlStmt));
/*
 * Create the Package Header
 */
strcpy( (char *) pSqlStmt, "CREATE PACKAGE ODBCRefCur AS\n");
strcat( (char *) pSqlStmt, " TYPE ename_cur IS REF CURSOR;\n");
strcat( (char *) pSqlStmt, " TYPE mgr_cur IS REF CURSOR;\n\n");
strcat( (char *) pSqlStmt, " PROCEDURE EmpCurs (Ename IN OUT ename_cur,");
strcat( (char *) pSqlStmt, "Mgr IN OUT mgr_cur,pjob IN VARCHAR2);\n\n");
strcat( (char *) pSqlStmt, "END;\n");
rc = SQLExecDirect(hStmt, pSqlStmt, strlen((char *)pSqlStmt));
if (rc != SQL_SUCCESS)
{
  DisplayError(SQL_HANDLE_STMT, hStmt, "SQLExecDirect");
}
/*
 * Create the Package Body
 */
strcpy( (char *) pSqlStmt, "CREATE PACKAGE BODY ODBCRefCur AS\n");
strcat( (char *) pSqlStmt, " PROCEDURE EmpCurs (Ename IN OUT ename_cur,");
strcat( (char *) pSqlStmt, "Mgr IN OUT mgr_cur, pjob IN VARCHAR2)\n AS\n  BEGIN\n");
strcat( (char *) pSqlStmt, " IF NOT Ename%ISOPEN\n THEN\n");
strcat( (char *) pSqlStmt, " OPEN Ename for SELECT ename from emp;\n");
strcat( (char *) pSqlStmt, " END IF;\n\n");
strcat( (char *) pSqlStmt, " IF NOT Mgr%ISOPEN\n THEN\n");
strcat( (char *) pSqlStmt, " OPEN Mgr for SELECT mgr from emp where job = pjob;\n");
strcat( (char *) pSqlStmt, " END IF;\n");
strcat( (char *) pSqlStmt, " END;\n");
strcat( (char *) pSqlStmt, "END;\n");
rc = SQLExecDirect(hStmt, pSqlStmt, strlen((char *)pSqlStmt));
if (rc != SQL_SUCCESS)
{
  DisplayError(SQL_HANDLE_STMT, hStmt, "SQLExecDirect");
}
/*
 * Bind the Parameter
 */
rc = SQLBindParameter(hStmt,1,SQL_PARAM_INPUT,SQL_C_CHAR,SQL_CHAR,JOB_LEN,0,pSalesMan,0,&sqlnts);
/*
 * Call the Store Procedure which executes the Result Sets
 */
strcpy( (char *) pSqlStmt, "{CALL ODBCRefCur.EmpCurs(?)}");
rc = SQLExecDirect(hStmt, pSqlStmt, strlen((char *)pSqlStmt));
if (rc != SQL_SUCCESS)
{
  DisplayError(SQL_HANDLE_STMT, hStmt, "SQLExecDirect");
}
/*
 * Bind the Data
 */
rc = SQLBindCol( hStmt,1,SQL_C_CHAR,Data,sizeof(Data),&DataLen);
if (rc != SQL_SUCCESS)
{
  DisplayError(SQL_HANDLE_STMT, hStmt, "SQLBindCol");
}
/*
 * Get the data for Result Set 1
 */
printf( "\nEmployee Names\n\n");
while ( rc == SQL_SUCCESS )
{
  rc = SQLFetch( hStmt );
  if ( rc == SQL_SUCCESS )
  {
    printf("%s\n", Data);
  }
  else
  {
    if (rc != SQL_NO_DATA)
    {
      DisplayError(SQL_HANDLE_STMT, hStmt, "SQLFetch");
    }
  }
}
printf( "\nFirst Result Set - Hit Return to Continue\n");
charptr = gets ((char *)error);
/*
 * Get the Next Result Set
 */
rc = SQLMoreResults( hStmt );
if (rc != SQL_SUCCESS)
{
  DisplayError(SQL_HANDLE_STMT, hStmt, "SQLMoreResults");
}
/*
 * Get the data for Result Set 2
 */
printf( "\nManagers\n\n");
while ( rc == SQL_SUCCESS )
{
  rc = SQLFetch( hStmt );
  if ( rc == SQL_SUCCESS )
  {
    printf("%s\n", Data);
  }
  else
  {
    if (rc != SQL_NO_DATA)
    {
    DisplayError(SQL_HANDLE_STMT, hStmt, "SQLFetch");
    }
  }
}
printf( "\nSecond Result Set - Hit Return to Continue\n");
charptr = gets ((char *)error);
/*
 * Should Be No More Results Sets
 */
rc = SQLMoreResults( hStmt );
if (rc != SQL_NO_DATA)
{
  DisplayError(SQL_HANDLE_STMT, hStmt, "SQLMoreResults");
}
/*
 * Drop the Package
 */
strcpy( (char *) pSqlStmt, "DROP PACKAGE ODBCRefCur");
rc = SQLExecDirect(hStmt, pSqlStmt, strlen((char *)pSqlStmt));
/*
 * Free handles close connections to the database
 */
SQLFreeHandle( SQL_HANDLE_STMT, hStmt );
SQLDisconnect( hDbc );
SQLFreeHandle( SQL_HANDLE_DBC, hDbc );
SQLFreeHandle( SQL_HANDLE_ENV, hEnv );
printf( "\nAll Done - Hit Return to Exit\n");
charptr = gets ((char *)error);
return(0);
}
/*
 * Display Error Messages
 */
void DisplayError( SWORD HandleType, SQLHANDLE hHandle, char *Module )
{
SQLCHAR MessageText[255];
SQLCHAR SQLState[80];
SQLRETURN rc=SQL_SUCCESS;
long NativeError;
SWORD RetLen;
SQLCHAR error[25];
char *charptr;
rc =
SQLGetDiagRec(HandleType,hHandle,1,SQLState,&NativeError,MessageText,255,&RetLen);
printf( "Failure Calling %s\n", Module );
if (rc == SQL_SUCCESS || rc == SQL_SUCCESS_WITH_INFO)
{
  printf( "\t\t\t State: %s\n", SQLState);
  printf( "\t\t\t Native Error: %d\n", NativeError );
  printf( "\t\t\t Error Message: %s\n", MessageText );
}
printf( "\nHit Return to Exit\n");
charptr = gets ((char *)error);
exit(1);
}

E.10 Enabling EXEC Syntax

If the syntax of the SQL Server EXEC statement can be readily translated to an equivalent Oracle procedure call without requiring any change to it, then 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:

The format for the name is:

[[[server.][database].][owner_name].]procedure_name

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

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.

E.11 Supported Functionality

This sections provides information about the functionality supported by Oracle ODBC Driver. It contains the following sections:

E.11.1 API Conformance

Oracle ODBC Driver release 10.2.0.1.0 and higher supports all Core, Level 2, and Level1 functions.

E.11.2 Implementation of ODBC API Functions

The following table describes 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.
SQLSpecialColumns If SQLSpecialColumns is called with the SQL_BEST_ROWID attribute, then it always returns the ROWID column.
SQLProcedures and SQLProcedureColumns Refer to the information in the following row.
All catalog functions If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, then 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, and not as a search pattern character. In contrast, if this attribute is set to SQL_FALSE, then it is either an ordinary argument or a pattern value argument and is treated literally, and its case is significant.

SQLProcedures and SQLProcedureColumns

The SQLProcedures and SQLProcedureColumns calls have been modified to locate and return information about all procedures and functions even if they are contained within a package. In earlier releases, the calls only found procedures and functions that were outside of packages. The following examples and scenarios show what procedures or functions are returned if the SQL_ATTR_METADATA_ID attribute is set to SQL_FALSE.

Suppose that you have the following stored procedures:

"BAR"
"BARX"
"XBAR"
"XBARX"
"SQLPROCTEST.BAR" 
"SQLPROCTEST.BARX" 
"SQLPROCTEST.XBAR" 
"SQLPROCTEST.XBARX" 

When you look for % or %%%%%%, you get all eight procedures.

When you look for %_ or _%, you get the following:

BAR 
BARX 
XBAR 
XBARX 

When you look for . or .% or %.% or SQLPROC%. or SQLPROC%.%, you get the following:

SQLPROCTEST.BAR
SQLPROCTEST.BARX 
SQLPROCTEST.XBAR 
SQLPROCTEST.XBARX 

When you look for %BAR, you get the following:

BAR
XBAR

When you look for .%BAR or %.%BAR, you get the following:

SQLPROCTEST.BAR
SQLPROCTEST.XBAR 

When you look for SQLPROC% or .SQLPROC%, you get the following:

nothing (0 rows)

E.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 set to SQL_NULL_DATA with SQLBindParameter, then the comparison fails. This is consistent with the null predicate syntax in ODBC SQL.

E.11.4 Implementation of Data Types

For programmers, the most important 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.

E.12 Unicode Support

This section provide information about Unicode support. It contains the following topics:

E.12.1 Unicode Support Within the ODBC Environment

ODBC Driver Manager makes all ODBC drivers, regardless of whether or not 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. Oracle ODBC Driver provides full Unicode support.

E.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 does not need to explicitly call entry points with the suffix. An ODBC application that is compiled with the UNICODE and _UNICODE preprocessor definitions will generate the appropriate calls. For example, a call to SQLPrepare will be 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 need to 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. In addition, Unicode encoding is also supported for SQL column types CHAR and VARCHAR2 if the character semantics are specified in the column definition.

Oracle ODBC Driver supports these SQL column types and maps them to ODBC SQL data types. The following table lists the supported SQL data types and the equivalent ODBC SQL data type:

SQL Data Types ODBC SQL Data Types
CHAR SQL_CHAR or SQL_WCHAR
VARCHAR2 SQL_VARCHAR or SQL_WVARCHAR
NCHAR SQL_WCHAR
NVARCHAR2 SQL_WVARCHAR
NCLOB SQL_WLONGVARCHAR

E.12.3 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 Oracle ODBC Driver to specify the data type before it is fetched. In this case, Oracle ODBC Driver uses information 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, then Oracle ODBC Driver must determine if it should fetch the column as Unicode or as the local code page. The driver could always 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, then there would be an ANSI to Unicode conversion to fetch the data into Oracle ODBC Driver. If the ODBC application then requested the data as SQL_C_CHAR, then there would be an additional conversion to revert the data to its original encoding.

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

E.12.4 Unicode Samples

Because Oracle ODBC Driver itself was implemented using TCHAR macros, it is recommended that ODBC application programs use TCHAR in order to take advantage of the driver.

The following examples show how to use TCHAR, which becomes the WCHAR data type if you compile with UNICODE and _UNICODE:

Example E-1 Connection to Database

To use this code, you only need to specify the Unicode literals for SQLConnect.

HENV         envHnd;
HDBC         conHnd;
HSTMT        stmtHnd;
RETCODE      rc;

rc  = SQL_SUCCESS;

// ENV is allocated
rc = SQLAllocEnv(&envHnd);
// Connection Handle is allocated
rc = SQLAllocConnect(envHnd, &conHnd);
rc = SQLConnect(conHnd, _T("stpc19"), SQL_NTS, _T("jones"), SQL_NTS, _T("password"), SQL_NTS);
.
.
.
if (conHnd)
  SQLFreeConnect(conHnd);
if (envHnd)
  SQLFreeEnv(envHnd);

Example E-2 Simple Retrieval

The following example retrieves the employee names and the job tiles 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, then you must specify the length of the buffer to the BYTE length when you call SQLBindCol. For example, sizeof(ename).

/*
** Execute SQL, bind columns, and Fetch.
** Procedure:
**
**   SQLExecDirect
**   SQLBindCol
**   SQLFetch
** 
*/
static SQLTCHAR *sqlStmt = _T("SELECT ename, job FROM emp");
SQLTCHAR   ename[50];
SQLTCHAR     job[50];
SQLINTEGER enamelen, joblen;
 
_tprintf(_T("Retrieve ENAME and JOB using SQLBindCol 1.../n[%s]/n"), sqlStmt);
 
// Step 1: Prepare and Execute
rc = SQLExecDirect(stmtHnd, sqlStmt, SQL_NTS); // select
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
// Step 2: Bind Columns
rc = SQLBindCol(stmtHnd,
                1,
                SQL_C_TCHAR,
                ename,
                sizeof(ename),
                &enamelen);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
rc = SQLBindCol(stmtHnd,
                2,
                SQL_C_TCHAR,
                job,
                sizeof(job),
                &joblen);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
do 
{
  // Step 3: Fetch Data
  rc = SQLFetch(stmtHnd);
  if (rc == SQL_NO_DATA)
    break;
  checkSQLErr(envHnd, conHnd, stmtHnd, rc);
  _tprintf(_T("ENAME = %s, JOB = %s/n"), ename, job);
} while (1);
_tprintf(_T("Finished Retrieval/n/n"));

Example E-3 Retrieval Using SQLGetData (Binding After Fetch)

This example shows how to use SQLGetData. There is no difference to the ANSI application in terms of Unicode-specific issues.

/*
** Execute SQL, bind columns, and Fetch.
** Procedure:
**
**   SQLExecDirect
**   SQLFetch
**   SQLGetData
*/
static SQLTCHAR *sqlStmt = _T("SELECT ename,job FROM emp"); // same as Case 1.
SQLTCHAR         ename[50];
SQLTCHAR         job[50];
 
_tprintf(_T("Retrieve ENAME and JOB using SQLGetData.../n[%s]/n"), sqlStmt);
if (rc != SQL_SUCCESS)
{
  _tprintf(_T("Failed to allocate STMT/n"));
  goto exit2;
}
 
// Step 1: Prepare and Execute
rc = SQLExecDirect(stmtHnd, sqlStmt, SQL_NTS); // select
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
do 
{
 
  // Step 2: Fetch
  rc = SQLFetch(stmtHnd);
  if (rc == SQL_NO_DATA)
    break;
  checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
  // Step 3: GetData
  rc = SQLGetData(stmtHnd, 
    1,
    SQL_C_TCHAR,
    (SQLPOINTER)ename,
    sizeof(ename), 
    NULL);
  checkSQLErr(envHnd, conHnd, stmtHnd, rc);
  rc = SQLGetData(stmtHnd, 
    2,
    SQL_C_TCHAR, 
    (SQLPOINTER)job,
    sizeof(job), 
    NULL);
  checkSQLErr(envHnd, conHnd, stmtHnd, rc);
  _tprintf(_T("ENAME = %s, JOB = %s/n"), ename, job);
} while (1);
_tprintf(_T("Finished Retrieval/n/n"));

Example E-4 Simple Update

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

/*
** Execute SQL, bind columns, and Fetch.
** Procedure:
**
**   SQLPrepare
**   SQLBindParameter
**   SQLExecute
*/
static SQLTCHAR *sqlStmt = _T("INSERT INTO emp(empno,ename,job) VALUES(?,?,?)");
static SQLTCHAR *empno   = _T("9876");      // Emp No
static SQLTCHAR *ename   = _T("ORACLE");    // Name
static SQLTCHAR *job     = _T("PRESIDENT"); // Job
 
_tprintf(_T("Insert User ORACLE using SQLBindParameter.../n[%s]/n"), sqlStmt);
 
// Step 1: Prepare
rc = SQLPrepare(stmtHnd, sqlStmt, SQL_NTS); // select
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
// Step 2: Bind Parameter
rc = SQLBindParameter(stmtHnd, 
                      1, 
                      SQL_PARAM_INPUT,
                      SQL_C_TCHAR,
                      SQL_DECIMAL,
                      4,               // 4 digit
                      0,
                      (SQLPOINTER)empno,
                      0,
                      NULL);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
rc = SQLBindParameter(stmtHnd, 
                      2, 
                      SQL_PARAM_INPUT,
                      SQL_C_TCHAR,
                      SQL_CHAR,
                      lstrlen(ename)*sizeof(TCHAR),
                      0,
                      (SQLPOINTER)ename,
                      lstrlen(ename)*sizeof(TCHAR),
                      NULL);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
rc = SQLBindParameter(stmtHnd, 
                      3, 
                      SQL_PARAM_INPUT,
                      SQL_C_TCHAR,
                      SQL_CHAR,
                      lstrlen(job)*sizeof(TCHAR),
                      0,
                      (SQLPOINTER)job,
                      lstrlen(job)*sizeof(TCHAR),
                      NULL);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
// Step 3: Execute
rc = SQLExecute(stmtHnd);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);

Example E-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 Database. Because the length of data should always be the BYTE length, the expression lstrlen(TCHAR data)*sizeof(TCHAR) is needed to derive the BYTE length.

/*
** Execute SQL, bind columns, and Fetch.
** Procedure:
**
**   SQLPrepare
**   SQLBindParameter
**   SQLExecute
**   SQLParamData
**   SQLPutData
**
**   SQLExecDirect
**   SQLFetch
**   SQLGetData
*/
static SQLTCHAR *sqlStmt1  = _T("INSERT INTO clobtbl(clob1) VALUES(?)");
static SQLTCHAR *sqlStmt2  = _T("SELECT clob1 FROM clobtbl");
SQLTCHAR         clobdata[1001];
SQLTCHAR         resultdata[1001];
SQLINTEGER       ind = SQL_DATA_AT_EXEC;
SQLTCHAR        *bufp;
int              clobdatalen, chunksize, dtsize, retchklen;
 
_tprintf(_T("Insert CLOB1 using SQLPutData.../n[%s]/n"), sqlStmt1);
 
// Set CLOB Data
{
  int i;
  SQLTCHAR ch;
  for (i=0, ch=_T('A'); i< sizeof(clobdata)/sizeof(SQLTCHAR); ++i, ++ch)
  {
    if (ch > _T('Z'))
      ch = _T('A');
    clobdata[i] = ch;
  }
  clobdata[sizeof(clobdata)/sizeof(SQLTCHAR)-1] = _T('/0');
}
clobdatalen = lstrlen(clobdata);  // length of characters
chunksize   = clobdatalen / 7;    // 7 times to put

// Step 1: Prepare
rc = SQLPrepare(stmtHnd, sqlStmt1, SQL_NTS);
checkSQLErr(envHnd, conHnd, stmtHnd, rc); 
// Step 2: Bind Parameter with SQL_DATA_AT_EXEC
rc = SQLBindParameter(stmtHnd, 
                      1, 
                      SQL_PARAM_INPUT,
                      SQL_C_TCHAR,
                      SQL_LONGVARCHAR,
                      clobdatalen*sizeof(TCHAR),
                      0,
                      (SQLPOINTER)clobdata,
                      clobdatalen*sizeof(TCHAR),
                      &ind);
checkSQLErr(envHnd, conHnd, stmtHnd, rc); 
// Step 3: Execute
rc = SQLExecute(stmtHnd);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
// Step 4: ParamData (initiation)
rc = SQLParamData(stmtHnd, (SQLPOINTER*)&bufp); // set value
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
for (dtsize=0, bufp = clobdata;
     dtsize < clobdatalen;
     dtsize += chunksize, bufp += chunksize)
{
  int len;
  if (dtsize+chunksize<clobdatalen)
    len = chunksize;
  else
    len = clobdatalen-dtsize;
 
  // Step 5: PutData
  rc = SQLPutData(stmtHnd, (SQLPOINTER)bufp, len*sizeof(TCHAR));
  checkSQLErr(envHnd, conHnd, stmtHnd, rc);
}
 
// Step 6: ParamData (temination)
rc = SQLParamData(stmtHnd, (SQLPOINTER*)&bufp);
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
rc = SQLFreeStmt(stmtHnd, SQL_CLOSE);
_tprintf(_T("Finished Update/n/n"));
rc = SQLAllocStmt(conHnd, &stmtHnd);
if (rc != SQL_SUCCESS)
{
  _tprintf(_T("Failed to allocate STMT/n"));
  goto exit2;
}
 
// Clear Result Data
memset(resultdata, 0, sizeof(resultdata));
chunksize   = clobdatalen / 15;   // 15 times to put
 
// Step 1: Prepare
rc = SQLExecDirect(stmtHnd, sqlStmt2, SQL_NTS); // select
checkSQLErr(envHnd, conHnd, stmtHnd, rc);
 
// Step 2: Fetch
rc = SQLFetch(stmtHnd);
checkSQLErr(envHnd, conHnd, stmtHnd, rc); 
for(dtsize=0, bufp = resultdata;
    dtsize < sizeof(resultdata)/sizeof(TCHAR) && rc != SQL_NO_DATA;
    dtsize += chunksize-1, bufp += chunksize-1)
{
  int len; // len should contain the space for NULL termination
  if (dtsize+chunksize<sizeof(resultdata)/sizeof(TCHAR))
    len = chunksize;
  else
    len = sizeof(resultdata)/sizeof(TCHAR)-dtsize;
 
  // Step 3: GetData
  rc = SQLGetData(stmtHnd, 
    1,
    SQL_C_TCHAR,
    (SQLPOINTER)bufp,
    len*sizeof(TCHAR), 
    &retchklen);
}
if (!_tcscmp(resultdata, clobdata))
{
  _tprintf(_T("Succeeded!!/n/n"));
}
else
{
  _tprintf(_T("Failed!!/n/n"));
}

E.13 Performance and Tuning

This section contains the following topics:

E.13.1 General ODBC Programming Guidelines

Apply the following programming guidelines 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 running it several times is much more efficient than preparing the statement for every SQLExecute.

  • Do not include columns in a SELECT statement of which you know the application will not retrieve; especially LONG columns. Because of the nature of the database server protocols, Oracle ODBC Driver must fetch the entire contents of a LONG column if it is included in the SELECT statement, regardless of whether the application binds the column or performs a SQLGetData operation.

  • If you are performing transactions that do not update the data source, then 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, then 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.

E.13.2 Data Source Configuration Options

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

  • 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.

    Oracle ODBC Driver must query the database server to determine the set of parameters for a procedure and their data types in order 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.

    Oracle 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 run.

    See Also:

    Oracle Database SecureFiles and Large Objects Developer's Guide for more information on LOBs

    Note:

    LOB data compression enables you to compress SecureFiles to gain disk, Input-Output, and redo logging savings. This reduces costs as compression utilizes space most efficiently and improves the performance of SecureFiles as compression reduces Input-Output and redo logging.

    LOB data encryption provides enhanced database security. While the encrypted data is available for random reads and writes, the data is more secure.

    Data compression and encryption consumes some additional memory.

  • Bind TIMESTAMP as DATE

    Binds SQL_TIMESTAMP parameters as the appropriate Oracle Database data type. If this option is set to TRUE, then SQL_TIMESTAMP binds as the Oracle DATE data type. If this option is set to FALSE, then 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 running the statement again without doing a SQLPrepare again. A typical scenario for this would be an application that expects to be idle for a while but will reuse the same SQL statement again. While the application is idle, it may want to free up any associated server resources.

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

    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 run the statement again without calling SQLPrepare. However, internally, Oracle ODBC Driver must prepare and run the statement all over. Enabling this option has a severe performance impact on applications that prepare a statement once and run it repeatedly.

    This option should only be enabled if freeing the resources on the server is necessary.

  • Fetch Buffer Size

    Set the Fetch Buffer Size (FetchBufferSize) in the odbc.ini file to a value specified in bytes. This value is the amount of memory needed that will determine how many rows of data Oracle ODBC Driver will pre-fetch at a time 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.

    There will be an improvement in the response time of applications that typically fetch fewer than 20 rows of data at a time, particularly over slow network connections or from heavily loaded servers. Setting this too high can have an adverse effect on response time or consume large amounts of memory. The default is 64,000 bytes. You should choose an optimal value for the application.

    When the LONG and LOB data types are present, the number of rows pre-fetched by Oracle 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. Oracle ODBC Driver ignores the Fetch Buffer Size and only pre-fetches a set number of rows in the presence of the LONG and LOB data types.

E.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, then there can be an impact on performance. For example:

SELECT * FROM EMP WHERE HIREDATE = ?

In this example, an index on the HIREDATE column could be used to make the query run quickly. However, because HIREDATE is a DATE value and Oracle ODBC Driver is supplying the parameter value as TIMESTAMP, the query optimizer of Oracle Database 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:

SELECT * FROM EMP WHERE TO_TIMESTAMP(HIREDATE) = ?

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

Note:

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

E.14 Error Messages

When an error occurs, 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 Oracle Database.

Native Error

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

SQLSTATE

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

Error Message

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

Error messages have the following format:

[vendor] [ODBC-component] [data-source] error-message

The prefixes in brackets ([ ]) identify the source of the error. The following table shows the values of these prefixes returned by 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.

Error Source Prefix Value
Driver Manager [vendor]

[ODBC-component]

[data-source]

[unixODBC]

[Driver Manager]

Not applicable

Oracle ODBC Driver [vendor]

[ODBC-component]

[data-source]

[ORACLE]

[Oracle ODBC Driver]

Not applicable

Oracle Database [vendor]

[ODBC-component]

[data-source]

[ORACLE]

[Oracle ODBC Driver]

[Oracle OCI]


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

[Oracle][ODBC]Error message text here

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

[Oracle][ODBC][Ora]Error message text here

Note:

Although the error message contains the Ora prefix, the actual error may originate from one of several sources.

If the error message text starts with the ORA- prefix, then you can obtain more information about the error in Oracle Database documentation.