您的格式已关闭，请记住需要DELIMITER $$语句，因为它与创建存储过程没有什么不同.

Your Formatting is off, remember DELIMITER $$ statements are required, as it is no different than creating a stored procedure.

在遇到此类问题时，请随时查阅文档

向下滚动文档约一半以查看示例.

Scroll about half way down the documents to see the example.

但是，这就是您要寻找的:

But, This is what your looking for:

DELIMITER $$
CREATE TRIGGER tg_newuser_insert 
BEFORE UPDATE ON tbl_newuser
FOR EACH ROW
    BEGIN

        SET NEW.id = CONCAT('YTUM', LPAD(LAST_INSERT_ID(), 8, '00000'));

    END $$
DELIMITER ;