访问表的价值，并在SQL

Question

我现在面临的麻烦与对抗的字符串 这里比较表1的值，它与一个字符串比较是什么香港专业教育学院尝试..

DELIMITER $$ 
DROP TRIGGER IF EXISTS comment_trigger$$ 
CREATE TRIGGER comment_trigger AFTER INSERT ON post_comments 
FOR EACH ROW 
DECLARE 
@var_post_id varchar(20); 
BEGIN 
IF (NEW.post_id LIKE 'rmdid%') THEN 
SET @var_post_id=SELECT post_id FROM recommendations WHERE recommendation_id=NEW.post_id; 
IF(@var_post_id LIKE 'recid%') THEN 
UPDATE cooking_category SET last_activity=NEW.comment_time WHERE post_id=NEW.post_id; 
END IF; 
END IF; 
END$$ 
DELIMITER ; 

有人可以帮助我请这个。

Answer 1

您可以将变量直接在select声明分配：

SELECT @var_post_id = post_id 
FROM recommendations 
WHERE recommendation_id=NEW.post_id; 

这是首选，但如果你把括号围绕select声明你的语法也将工作：

SET @var_post_id=(SELECT post_id FROM recommendations WHERE recommendation_id=NEW.post_id);