[英]How to insert COUNT value of another table in column of a table
INSERT INTO Destination(Col)
SELECT COUNT(1) FROM Source;
您可以使用觸發器根據likes
表自動更新comments
表。
AFTER觸發器在插入以下,這將增加的價值total_likes
相應的comment_id by
在一個comments
時進行的插入表likes
表。
插入comments
表時,必須將comments
的total_likes
初始值設置為零。
CREATE TRIGGER update_likes AFTER INSERT ON likes
FOR EACH ROW
UPDATE comments
SET total_likes = total_likes+1
WHERE comment_id = NEW.comment_id;
如果要查詢解決此問題。 我建議像這樣:
select comment_id,uploader,
(select count(*) from likes l where L.COMMENT_ID =CM.COMMENT_ID ) nlikes
from commments cm;
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