存储过程在更新之前检查值

Question

我正在尝试创建一个存储过程，如果有任何更改，则检查IN值，如果有继续更新，否则不要更新。

 CREATE DEFINER=`root`@`localhost` PROCEDURE `new_procedure`(
 IN id_ INT,
 IN data1_ VARCHAR(45),
 IN data2_ VARCHAR(45)
 )
 BEGIN
 DECLARE data1check varchar(45);
 DECLARE data2check varchar(45);

 SELECT data1, data2 FROM main AS B;
 SET data1check = B.data1;
 SET data2check = B.data2;

 IF (data1check <> data1_ OR data2check <> data2_)

 THEN

    UPDATE main SET 
    version = version + 1,
    data1 = COALESCE(data1_, data1), 
    data2 = COALESCE(data2_, data2) 
    WHERE id = id_;

 END IF;
 END

我用这个查询试了一下：

CALL new_procedure(1,'Violet','Green')

但我明白了：

Error Code: 1109 Unknown table 'B' in field list

Answer 1

你试过用过吗？

SET data1check = main.data1;
SET data2check = main.data2;

而不是

SET data1check = B.data1;
SET data2check = B.data2;