带有声明的 MySQL 动态查询

Question

我想问一下是否可以在动态查询中使用DECLARE 变量。

即：

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

但我收到语法错误：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

谢谢

Answer 1

• 首先 - DECLARE 只允许在 BEGIN ... END 复合语句中。
• 第二 - 不是所有的状态都可以在 PREPARE 语句中使用，更多细节在这里 - Prepared Statements。

但是你可以使用这样的东西 -

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 |
+-----------+