qdb_stmt_init()

Updated: May 06, 2022

Initialize a prepared statement

Synopsis:

#include <qdb/qdb.h>

int qdb_stmt_init( qdb_hdl_t *db, const char *sql, uint32_t len );

Arguments:

db
A pointer to the database handle.
sql
An SQL statement. This statement may contain variable parameters of the form ?n, where n is a number between 1 and 999. These placeholders can be filled in with data on a subsequent call to qdb_stmt_exec().
len
The length of sql.

Library:

qdb

Description:

This function initializes a prepared (precompiled) SQL statement. A prepared statement is compiled once but can be executed multiple times. This function returns a statement ID for the prepared statement, which you must then pass in to qdb_stmt_exec().

QDB executes precompiled statements faster than uncompiled statements, so this approach can optimize your application's performance when executing frequently used statements.

You can free prepared statements using qdb_stmt_free(), although all such statements are freed when you call qdb_disconnect().

Returns:

>=0
Success. The returned value is the prepared statement's ID. Note that 0 is a valid ID.
-1
An error occurred (errno is set).

Examples:

The following code sample shows how to compile, execute, and free an SQL statement:

int stmtid;
qdb_binding_t qbind[2];
uint64_t msid, limit;

const char *sql = "SELECT fid FROM library WHERE msid=?1 LIMIT ?2;";

stmtid = qdb_stmt_init(db, sql, strlen(sql)+1);

if (stmtid == -1) {
     // Could not compile
     return -1;
}

msid = 1;
limit = 10;
QDB_SETBIND_INT(&qbind[0], 1, msid);
QDB_SETBIND_INT(&qbind[1], 2, limit);

if (qdb_stmt_exec(db, stmtid, qbind, 2) == -1) {
     // Could not execute
     return -1;
}

qdb_stmt_free(db, stmtid);

Note the +1 added to the length of the string returned by strlen() (which is used in the call to qdb_stmt_init()); this sends QDB the final NULL character required for a valid string.

Classification:

QNX Neutrino

Safety:  
Interrupt handler No
Signal handler No
Thread Yes