我正在尝试简化我的查询,以便它只包含一次会话ID(SID)。
Users表的抽象结构是:
+----+------+----------+
| ID | Name | Username |
+----+------+----------+
Friends表有一个抽象结构,如:
+----+-----------------+----------+--------+---------+
| ID | UserID | FriendID | Hidden | Deleted |
| | (Foreign key | | | |
| | of ID in Users) | | | |
+----+-----------------+----------+--------+---------+
Sessions表的抽象结构:
+----+-----------------+-----+
| ID | UserID | SID |
| | (Foreign key | |
| | of ID in Users) | |
+----+-----------------+-----+
我有以下查询,它是根据我之前的一个问题的答案改编的。如您所见,会话ID(SID)重复4次,是否可以将查询压缩为一个整体,以便只需要一次SID?
SELECT *
,CASE
WHEN D.ID IS NULL
THEN "Wants to be your friend"
ELSE "Friends"
END AS STATUS
FROM (
SELECT DISTINCT A.ID
,A.NAME
,E.Hidden
FROM Users A
INNER JOIN Friends E ON A.ID = E.UserID
WHERE A.ID IN (
SELECT A.UserID
FROM Friends A
INNER JOIN Sessions S ON A.FriendID = S.UserID
WHERE S.SID = "1234"
AND Deleted = 'No'
)
) C
LEFT JOIN (
SELECT DISTINCT B.ID
,B.NAME
,F.Hidden
FROM Users B
INNER JOIN Friends F ON B.ID = F.FriendID
WHERE B.ID IN (
SELECT A.FriendID
FROM Friends A
INNER JOIN Sessions S ON A.UserID = S.UserID
WHERE S.SID = "1234"
AND Deleted = 'No'
)
) D ON C.ID = D.ID
UNION
DISTINCT
SELECT *
,CASE
WHEN C.ID IS NULL
THEN "Request Sent"
ELSE "Friends"
END AS STATUS
FROM (
SELECT DISTINCT A.ID
,A.NAME
,E.Hidden
FROM Users A
INNER JOIN Friends E ON A.ID = E.UserID
WHERE A.ID IN (
SELECT A.UserID
FROM Friends A
INNER JOIN Sessions S ON A.FriendID = S.UserID
WHERE S.SID = "1234"
AND Deleted = 'No'
)
) C
RIGHT JOIN (
SELECT DISTINCT B.ID
,B.NAME
,F.Hidden
FROM Users B
INNER JOIN Friends F ON B.ID = F.FriendID
WHERE B.ID IN (
SELECT A.FriendID
FROM Friends A
INNER JOIN Sessions S ON A.UserID = S.UserID
WHERE S.SID = "1234"
AND Deleted = 'No'
)
) D ON C.ID = D.ID
解释系统的基本方法是,如果两个用户是朋友,那么数据库中有两条记录。一个从第一个用户到另一个用户,另一个记录从第二个用户到第一个用户。
如果有当前用户到另一个用户的记录,则已发送好友请求,如果有一个用户到当前用户的记录,则已收到好友请求。
这是一个如何运作的范围图:
SQL小提琴 - http://sqlfiddle.com/#!2/c5587/1
答案 0 :(得分:0)
Sql fiddle:http://sqlfiddle.com/#!2/06e08/68/0
此返回Friends and Request Sent
:
SELECT
f.FriendID,
u.Name,
f.Hidden,
CASE
WHEN reqs.FriendID IS NULL
THEN "Request Sent"
WHEN reqs.FriendID = f.UserID
THEN "Friends"
END AS Status
FROM
Friends AS f
INNER JOIN
Sessions AS s
ON f.UserId = s.UserID
INNER JOIN
Users AS u
ON u.ID = f.FriendID
LEFT JOIN
Friends AS reqs
ON reqs.FriendID = f.UserID
AND reqs.UserID = f.FriendID
WHERE
s.SID = "sid1"
如果您还需要Request Received
,请附加:
UNION
SELECT
f.UserID,
u.Name,
f.Hidden,
"Request Received" AS Status
FROM
Friends AS f
INNER JOIN
Sessions AS s
ON f.FriendID = s.UserID
INNER JOIN
Users AS u
ON u.ID = f.UserID
WHERE
f.UserID NOT IN
(
SELECT
ff.FriendID
FROM
Friends AS ff
INNER JOIN
Sessions AS ss
ON ff.UserID = ss.UserID
WHERE ss.SID = "sid1"
)
AND s.SID = "sid1"
无法弄清楚如何优化最后一部分。因为它是一个自我加入,它是一个该死的心灵缠绕。
我知道这不是您的预期,但我无法驾驭所有SID,但此请求应该比您目前使用的请求更快