Question

I would like to ask if it is possible to DECLARE variables in dynamic queries.

i.e.:

CREATE PROCEDURE `storedProcedureName`()
    DETERMINISTIC
    SQL SECURITY DEFINER
    COMMENT ''
BEGIN

    SET @i = 0;

    PREPARE dynamicQuery FROM 'DECLARE x INT(11);';
    EXECUTE dynamicQuery;

    PREPARE dynamicQuery FROM 'SET x := ?;';
    EXECUTE dynamicQuery USING @i;

    DEALLOCATE PREPARE dynamicQuery;

    /* More Queries Here */

END

But I’m getting syntax error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE x INT(11)' at line 1

Thanks

Answer 1

• First – DECLARE is allowed only inside a BEGIN … END compound statement.
• Second – not all stataments can be used in PREPARE statement, more details here – Prepared Statements.

But you can use something like this –

SET @text = 'something';
SET @var = NULL;
SET @query = 'SELECT ? INTO @var';
PREPARE s FROM @query;
EXECUTE s USING @text;
DEALLOCATE PREPARE s;

SELECT @var;
+-----------+
| @var      |
+-----------+
| something |
+-----------+