触发器内select语句中的MySQL错误

Question

我最近开始使用MySQL n，现在我想创建一个触发器，但是MySQL在我的语法中返回一个错误。

delimiter $$; 
create trigger abc after insert on ratings 
for each row 
    begin 
     set @n1 = select avg(rating) from ratings join users where ratings.uname=users.uname 
     and ratings.bookid=new.bookid users.`type`='admin' or users.`type`='critic'; 
     update books set avgcriticrating = @n1 where bookid=new.bookid; 
end; 

select语句在单独触发时运行良好，但在触发器内部使用时发生错误。

这里的错误是，MySQL提供了

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'select avg(rating) from ratings join users where ratings.uname=users.uname an' at line 4 

无论是书籍和评级表包含一个称为BOOKID场。

请帮助

Answer 1

如果你想从一个select语句一个值，该语句是在（括号内）。会发生在new.bookid users

set @n1 = (select avg(rating) from ratings join users where ratings.uname=users.uname 
    and ratings.bookid=new.bookid users.`type`='admin' or users.`type`='critic'); 

下一个错误 - 有可能是一个and或or失踪。