SQLPrepare() and SQLExecute()—Prepare and Execute Queries
For queries that are executed multiple times, preparing the queries before execution may improve performance because the DBMS stores the query plan of prepared queries. Rather than calculating a query plan each time a query is executed, the DBMS references the query plan for all subsequent iterations of the query.
SQLPrepare() and SQLExecute() perform the prepare and execute functions, respectively.
Unless the ODBC application explicitly prepares a query via SQLPrepare(), the ODBC always executes queries directly; there is no provision for automatically preparing queries in Ingres.
The following code snippet is the equivalent of the SQLExecDirect() code example in the Execute Queries Directly section.
Example: SQLPrepare() and SQLExecute() Functions
/* Prepare a "create table" query. */
SQLPrepare( hstmt, "create table cars( model varchar(20) )",
SQL_NTS );
/* Execute the prepared query */
SQLExecute(hstmt);
Prepared queries persist in the default autocommit state. However, if you turn off autocommit via SQLSetConnectAttr(), the query plan associated with a prepared query is destroyed whenever the query is rolled back or committed. You must then re-prepare the query via SQLPrepare().