sql - 查询是否已添加好友

Question

我有一个存储 users 表的用户 ID 和 user_friend_id 列的朋友表。

如果我想阻止添加已经由特定用户 ID 添加的朋友，我应该写什么查询？

UserId UserFriendId
1      12
1      13
1      15
2      14
2      17

Answer 1

如果结果 ( totalCount) 的值大于零，则表示两个人已经是朋友。

SELECT COUNT(*) totalCount
FROM    tableName
WHERE   (userID = yourID AND UserFriendID = friendID) OR
        (userID = friendID AND UserFriendID = yourID)

Answer 2

insert into friends (userId, userFriendId)
select 1, 12
where not exists (
    select 1 from friends where userId = 1 and userFriendId = 12
)

Answer 3

只需创建具有 3 个参数的存储过程，如下所示：

CREATE PROCEDURE AddUserFriends
@UserID int,
@FriendID int,
@ExcludeUserID int -- the userid you want to exclude adding his friends
AS
BEGIN
INSERT INTO UserFriends(UserID, FriendID)
SELECT @UserID, @FriendID
WHERE @FriendID NOT IN(SELECT FriendID FROM UserFriends WHERE UserID=@ExcludeUserID)
END