MySQL Remove repeating clauses in subqueries - mysql

Question

I'm trying to simplify my query so that it only contains the session ID (SID) once.
The abstract structure of the Users table is:
+----+------+----------+
| ID | Name | Username |
+----+------+----------+
The Friends table has an abstract structure like:
+----+-----------------+----------+--------+---------+
| ID | UserID | FriendID | Hidden | Deleted |
| | (Foreign key | | | |
| | of ID in Users) | | | |
+----+-----------------+----------+--------+---------+
The abstract structure of the Sessions table:
+----+-----------------+-----+
| ID | UserID | SID |
| | (Foreign key | |
| | of ID in Users) | |
+----+-----------------+-----+
I have the following query, which has been adapted from the answer of a previous question of mine. As you can see, the session ID (SID) is repeated 4 times, is it possible to condense the query as a whole so that the SID is only required once?
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
A basic way of explaining the system is that if two users are friends, then there is two records within the database. One from the first user to the second and another record from the second user to the first.
A friend request has been sent if there is a record from the current user to another, and a friend request has been received if there is a record from one user to the current one.
Here is a vann diagram of how it works:
SQL Fiddle - http://sqlfiddle.com/#!2/c5587/1

Answer 1

Sql fiddle : http://sqlfiddle.com/#!2/06e08/68/0
This return 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"
If you want Also Request Received, append this :
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"
Can't figure out how to optimise the last part. Since it's a SELF JOIN it's a damn mind twister.
I understand this is not what you expected but, i can't get ride of all the SID, but this request should be faster than the one you currently use