mysql - sql 触发器在变量中存储列名并将其用于 sql 触发器中的 OLD.myvar 时出现错误

Question

MySQL 说:#1054 - “OLD”中存在未知列“TMPCOL”

BEGIN
DECLARE TOTAL,I INT;
DECLARE CURRENT_CLOUMN VARCHAR(255);
DECLARE TRIGGER_ON_TABLE VARCHAR(255);
DECLARE TRIGGER_OP VARCHAR(255);
DECLARE olddd VARCHAR(255);
DECLARE newwww VARCHAR(255);
SET TOTAL=0;
SET I=0;
SET CURRENT_CLOUMN='atulbaldaniya.com';
SET TRIGGER_ON_TABLE='atulbaldaniya';
SET TRIGGER_OP='UPDATE';
SET olddd='';
SET newwww='';

SELECT COUNT(COLUMN_NAME) INTO  TOTAL  FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = TRIGGER_ON_TABLE ORDER BY ORDINAL_POSITION;
    WHILE I < TOTAL DO
        SELECT COLUMN_NAME INTO CURRENT_CLOUMN FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = TRIGGER_ON_TABLE ORDER BY ORDINAL_POSITION LIMIT I,1;
        SET olddd=OLD.CURRENT_CLOUMN;
        SET newwww=NEW.CURRENT_CLOUMN;
            IF(olddd != newwww) THEN
                INSERT INTO TMP(DATA1, DATA2)VALUES(TOTAL ,CONCAT('Change in ',olddd,' To ',newwww))
            END IF; 
        SET I=I+1;
    END WHILE ;
END

我不想
INSERT INTO TMP(DATA1, DATA2)VALUES(TOTAL,OLD.ID);
这工作正常。

我想将列名称存储在变量中并使用 OLD.MYVAR

我们怎样才能这样做呢？

Answer 1

您可以将查询构建为字符串，然后准备并执行它，类似于:

SET @s = CONCAT('INSERT INTO TMP(DATA1, DATA2) VALUES ("DATA",OLD.',TMPCOL,');');

PREPARE stmt1 FROM @s;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;