带有if语句的MYSQL触发器

我好像没办法让这个扳机动起来

 CREATE TRIGGER class_check BEFORE INSERT ON Category
 DECLARE x VARCHAR(1);
 SET x = (SELECT Type1 FROM Category);
 IF (x<>'A') THEN
 CALL `'ERROR'`;
 END IF;
 IF (NEW.MxLen > 3 AND x ='M') THEN
 CALL `'ERROR LENGTH MUST BE LESS THAN 3 FOR M CLASS LICENSE'`;
 ELSEIF (NEW.MxLen > 5 AND x ='G') THEN
 CALL `'ERROR LENGTH MUST BE LESS THAN 5 FOR G CLASS LICENSE'`;
 ELSEIF (NEW.MxLen > 30) THEN
 CALL `'ERROR LENGTH MUST BE LESS THAN 30 FOR A,B,C,D,E CLASS LICENSE'`;
 END IF;

上面的触发器没有按我希望的方式工作，我似乎找不到问题所在。 基本上，我想让它检查Category表中的type1是否不是A，然后抛出一个错误。每次我尝试添加一个，它仍然会抛出错误。

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任何帮助都将不胜感激。更新前我也有相同的标记。

反勾号转义了它们之间的名称，表示这是一个标识符。我怀疑你是否真的有这些名字的标识符。只需对字符串使用单引号：

通常，调用后面会有存储过程名。我猜您确实希望信号引发错误：

CREATE TRIGGER class_check BEFORE INSERT ON Category
 DECLARE x VARCHAR(1);
 SET x = (SELECT Type1 FROM Category);
 IF (x <> 'A') THEN
     SIGNAL '45000' SET MESSAGE_TEXT = 'ERROR';
 END IF;
 IF (NEW.MxLen > 3 AND x ='M') THEN
     SIGNAL '45000' SET MESSAGE_TEXT = 'ERROR LENGTH MUST BE LESS THAN 3 FOR M CLASS LICENSE';
 ELSEIF (NEW.MxLen > 5 AND x ='G') THEN
     SIGNAL '45000' SET MESSAGE_TEXT = 'ERROR LENGTH MUST BE LESS THAN 5 FOR G CLASS LICENSE';
 ELSEIF (NEW.MxLen > 30) THEN
     SIGNAL '45000' SET MESSAGE_TEXT = 'ERROR LENGTH MUST BE LESS THAN 30 FOR A,B,C,D,E CLASS LICENSE';
 END IF;

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如果类别中有多行，则可能返回错误。

您会收到哪条错误消息？对于A、B、C、D、E类许可证，可能错误长度必须小于30？我得到第一个错误“ERROR”

 SET x = (SELECT Type1 FROM Category);