[英]Turn subquery into join query
對於此查詢:
SELECT `user_id`, `user_name` FROM users WHERE `user_id` IN (SELECT user_one, user_two FROM friends WHERE user_one='$my_id' OR user_two = '$my_id')
我收到此錯誤消息:
基數違規:1241操作數應包含1列
是否可以在連接中使用2列而不是子查詢? 如果是,怎么樣?
為什么不使用這樣的聯盟:
SELECT `user_id`, `user_name`
FROM users
WHERE `user_id` IN (SELECT user_one FROM friends
where user_one = '$my_id'
UNION
SELECT user_two FROM friends
where user_two = '$my_id')
如果您希望user_id位於user_one或users_two的friends
表中的users
表中的記錄,您可以執行以下操作:
SELECT `user_id`, `user_name`
FROM users
WHERE `user_id` IN (
SELECT user_one
FROM friends
WHERE user_one = '$my_id'
)
UNION ALL
SELECT `user_id`, `user_name`
FROM users
WHERE `user_id` IN (
SELECT user_two
FROM friends
WHERE user_two = '$my_id'
);
從用戶選擇a.userid,a.username a.userid = b.userid中的內部聯接朋友b,其中b.user_one ='$ my_id'或b.user_two ='$ my_id'
嘗試這個:
SELECT user_id, user_name FROM users U
join friends F
ON F.user_id=U.user_id
and F.user_name=U.user_name
WHERE F.user_one='$my_id' OR F.user_two = '$my_id'
您的查詢返回錯誤,因為IN子句無法在where語句中的多個列上進行選擇。
我認為你在尋找的東西可能是這樣的
SELECT
user_id,
user_name
FROM users INNER JOIN Friends ON Users.User_ID = User_one OR Users.User_ID = User_Two
SELECT user_id,user_name FROM users a,friends b WHERE a.user_id = b.user_one AND(b.user_one ='$ my_id'OR b.user_two ='$ my_id')
IN操作數只接受一個參數。 如果你想得到你所有的朋友,你需要以只返回一列的方式這樣做。 您可以使用UNION執行類似的操作:
SELECT user_one
FROM friends
WHERE user_two = 'me'
UNION
SELECT user_two
FROM friends
WHERE user_one = 'me';
然后,將其用作IN參數:
SELECT user_id, user_name
FROM users
WHERE user_id IN(
SELECT user_one
FROM friends
WHERE user_two = 'me'
UNION
SELECT user_two
FROM friends
WHERE user_one = 'me');
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