从触发器调用的存储过程中动态语句的解决方法 [英] Workaround for dynamic statements in stored procedures called from triggers

问题描述

Mysql PREPARE和EXECUTE语句不能在触发器调用的存储过程中使用.结果将为Error Code: 1336. Dynamic SQL is not allowed in stored function or trigger.

Mysql PREPARE and EXECUTE statements can not be used in a stored procedure that is being called by a trigger. The result would be Error Code: 1336. Dynamic SQL is not allowed in stored function or trigger.

有人知道在这方面可行的工作吗?

Does anyone know a plausible work around to this?

推荐答案

您不能在TRIGGER内部运行PREPARE/EXECUTE，但是可以在EVENT中运行(如果您正在运行MySQL， 5.5或更高).

You can't run PREPARE/EXECUTE from inside a TRIGGER, but you can from an EVENT (if you are running MySQL 5.5 or greater).

这是从EVENT运行PREPARE/EXECUTE的示例:

DROP TABLE IF EXISTS tbl1;
DROP TABLE IF EXISTS tbl2;
DROP TABLE IF EXISTS cmds;
DROP PROCEDURE IF EXISTS proc;
DROP TRIGGER IF EXISTS trig;

CREATE TABLE tbl1 (i INT, v VARCHAR(255));
CREATE TABLE tbl2 (i INT, v VARCHAR(255));

CREATE TABLE cmds (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    done BOOL NOT NULL DEFAULT FALSE,
    cmd TEXT,
    PRIMARY KEY (id),
    INDEX (done, id)
);

DELIMITER //

CREATE PROCEDURE proc()
NOT DETERMINISTIC
MODIFIES SQL DATA
proc: BEGIN
    DECLARE b_not_found     BOOL DEFAULT FALSE;
    DECLARE i_id            INT UNSIGNED;
    DECLARE t_cmd           TEXT;
    DECLARE v_lock_name     VARCHAR(255) DEFAULT 'proc_lock';

    DECLARE cur CURSOR FOR
        SELECT id, cmd FROM cmds WHERE NOT done ORDER BY id;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET b_not_found = TRUE;

    IF (NOT GET_LOCK(v_lock_name, 0)) THEN
        LEAVE proc;
    END IF;

    OPEN cur;

    loop1: LOOP
        FETCH cur INTO i_id, t_cmd;
        IF b_not_found THEN
            LEAVE loop1;
        END IF;

        SET @cmd = t_cmd;

        PREPARE stmt FROM @cmd;
        EXECUTE stmt;
        DROP PREPARE stmt;

        UPDATE cmds SET done = TRUE WHERE id = i_id;
    END LOOP;

    CLOSE cur;

    DO RELEASE_LOCK(v_lock_name);
END;
//

CREATE TRIGGER trig
    BEFORE INSERT ON tbl1
    FOR EACH ROW
BEGIN
    INSERT INTO cmds SET cmd = 
        CONCAT("INSERT INTO tbl2 SET i = ", -NEW.i, ", v = ", QUOTE(NEW.v));
END;
//

DROP EVENT IF EXISTS evnt //

CREATE EVENT evnt
ON SCHEDULE 
EVERY 1 SECOND
DO
BEGIN
    CALL proc();
END;
//

DELIMITER ;

SET GLOBAL event_scheduler = 1;

然后运行:

INSERT INTO tbl1 VALUES (UNIX_TIMESTAMP(), 'ex 1');
DO SLEEP(2);
INSERT INTO tbl1 VALUES (UNIX_TIMESTAMP(), 'ex 2');
DO SLEEP(1);
SELECT * FROM tbl2;

将产生以下输出:

+-------------+------+
| i           | v    |
+-------------+------+
| -1348550619 | ex 1 |
| -1348550621 | ex 2 |
+-------------+------+
2 rows in set (0.00 sec)

如果您不想使用EVENT，或者等待一秒钟左右才能触发它，则可以在每个会导致TRIGGER触发的命令之后添加一个CALL proc().

If you don't want to use an EVENT, or wait the second or so for it to fire, you could add a CALL proc() after every command that would cause a TRIGGER to fire.

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