mySQL 比较触发器中的两个不同列值

Question

I am trying to have a trigger check if two values in a table are the same and if so insert the information into another table. My code is below.

user_id is a INT(10) post_author_id is a VARCHAR(33) 8utf_unicode_ci

CASE
WHEN (new.user_id = (SELECT CAST(post_author_id AS UNSIGNED INTEGER) FROM Cvr_hooks_501_1000)) 
THEN
INSERT INTO Cvr_1_link_501_1000 (a_hook_id, a_user_id, a_post_id, a_post_author_id)

VALUES (new.hook_id, 
        new.user_id, 
        new.post_id, 
        new.post_author_id);

END CASE

Any help is appreciated!

Answer 1

You can use EXISTS to check if the user already existst

CREATE tABLE Cvr_hooks_501_1000(post_author_id vaRCHAR(39))

 INSERT INTO Cvr_hooks_501_1000 VALUES ("1")

 CREATE TABLE account(hook_id int, user_id int(11) ,post_id int, post_author_id int)

 CREATE TABLE Cvr_1_link_501_1000 (a_hook_id int, a_user_id int(11) ,a_post_id int, a_post_author_id int)

 CREATE TRIGGER upd_check AFTER INSERT ON account FOR EACH ROW BEGIN IF ( EXISTS(SELECT 1 FROM Cvr_hooks_501_1000 WHERE post_author_id = new.user_id)) then INSERT INTO Cvr_1_link_501_1000 (a_hook_id, a_user_id, a_post_id, a_post_author_id) VALUES (new.hook_id, new.user_id, new.post_id, new.post_author_id); END IF; END

 INSERT INTO account VALUES(1,1,1,1)

 SELECT * FROM Cvr_1_link_501_1000

\na_hook_id |  a_user_id |  a_post_id |  a_post_author_id \n--------: |  --------: |  --------: |  ---------------: \n        1 |  1 |  1 |  1 \n

db<>fiddle here