How to pass parent field in sub union query - mysql

Question

I've this query and its giving an error that unknown U.UserID column in where clause but I can't see any error in it as my Users table instance is U
SELECT GROUP_CONCAT(U.UserID),
(
SELECT COUNT(DISTINCT(UserID))
FROM (
SELECT FriendID as UserID
FROM Friends
WHERE UserID=U.UserID AND Status=1
UNION All
SELECT UserID
FROM Follow
WHERE Type='user' AND TypeEntityID=U.UserID
) tbl
) as NoOfFriendsFollow
FROM `Users` `U`
WHERE `U`.`UserID` IN('1')
LIMIT 10
Any solution for this query or let me know where I'm wrong

Answer 1

SELECT GROUP_CONCAT(UserID),
(
SELECT COUNT(DISTINCT(UserID)) FROM
(
SELECT FriendID as UserID FROM Friends F
INNER JOIN Users U ON U.UserID=F.FriendID
WHERE F.Status=1
UNION All
SELECT FF.UserID FROM Follow FF
INNER JOIN Users U ON U.UserID=FF.UserID
WHERE Type='user' AND TypeEntityID=U.UserID
) tbl
) as NoOfFriendsFollow
FROM Users WHERE UserID IN('1') LIMIT 10;
Just try above code.
Hope this will helps.

Answer 2

Unfortunately, MySSQL does not permit you to use an outer table reference "two levels down". So you can do:
SELECT U.UserID,
(SELECT COUNT(DISTINCT UserID)
FROM (SELECT fr.FriendID as UserID, fr.FriendId as compareId
FROM Friends fr
WHERE fr.Status = 1
UNION All
SELECT f.UserID, f.TypeEntityID as compareId
FROM Follow f
WHERE f.Type = 'user'
) tbl
WHERE tbl.UserID = compareId
) as NoOfFriendsFollow
FROM Users U
WHERE U.UserID IN (1)
LIMIT 10;
Notes:
This moves the comparison into the middle subquery, so the query parses.
Presumably UserId is an integer. Only use single quotes for string and date constants.
The GROUP_CONCAT() doesn't make sense. It turns the query into an aggregation query that returns only one row.
I double the LIMIT is needed either. There should be one row per UserId.
Always use qualified column names when you have multiple tables in a query.