mysql - 为什么不能在存储过程中使用变量作为表名？

我试图使用一个变量作为存储过程中的表名，它使用它作为字符串文字，而不是实际的表名。这是为什么？有没有其他方法我应该这样做（除了只是在PHP中做）？

DROP PROCEDURE IF EXISTS settonull;

DELIMITER //

CREATE PROCEDURE settonull()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE _tablename VARCHAR(255);
  DECLARE _columnname VARCHAR(255);
  DECLARE cur1 CURSOR FOR SELECT CONCAT(TABLE_SCHEMA, '.', TABLE_NAME) AS table_name, COLUMN_NAME AS column_name FROM information_schema.COLUMNS WHERE IS_NULLABLE = 'YES' AND TABLE_SCHEMA = 'blip_notify' AND table_name = 'notify_queue' LIMIT 1;

  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  OPEN cur1;

  read_loop: LOOP
    FETCH cur1 INTO _tablename, _columnname;

    IF done THEN
      LEAVE read_loop;
    END IF;

    UPDATE _tablename SET _columnname = NULL WHERE LENGTH(TRIM(_columnname)) = 0;

  END LOOP;

  CLOSE cur1;
END//

DELIMITER ;

CALL settonull();

输出：

0 row(s) affected, 1 warning(s)

Execution Time : 0 sec
Transfer Time  : 1.094 sec
Total Time     : 1.095 sec

Note Code : 1305
PROCEDURE settonull does not exist
---------------------------------------------------

0 row(s) affected

Execution Time : 0.002 sec
Transfer Time  : 1.011 sec
Total Time     : 1.014 sec
---------------------------------------------------

Query: call settonull()

Error Code: 1146
Table 'blip_notify._tablename' doesn't exist

Execution Time : 0 sec
Transfer Time  : 0 sec
Total Time     : 0.003 sec
---------------------------------------------------

最佳答案

您需要使用动态sql。是的，呃。

SET @s = CONCAT('UPDATE ', _tablename, ' SET ', _columnname, ' = NULL WHERE LENGTH(TRIM(', _columnname, ')) = 0' );
PREPARE stmt FROM @s;
EXECUTE stmt;

关于mysql - 为什么不能在存储过程中使用变量作为表名？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/8363415/