Counting rows from a subquery

Question

How could I count rows from a SELECT query as a value? Such as

SELECT FUCNTIONIMLOOKINGFOR(SELECT * FROM anothertable) AS count FROM table;

So that count is an integer of how many rows the subquery SELECT * FROM anothertable returns.

EDIT

SELECT p.PostPID, p.PostUID, p.PostText, p.PostTime, u.UserUID, u.UserName, u.UserImage, u.UserRep,
    (
        SELECT COUNT(f.FlagTime)
            FROM Flags as f 
                JOIN Posts as p 
                ON p.PostPID = f.FlagPID
    ) as PostFlags
    FROM Posts AS p
        JOIN Users AS u
        ON p.PostUID = u.UserUID
    ORDER BY PostTime DESC
    LIMIT 0, 30

Answer 1

SELECT ( SELECT COUNT(id) FROM aTable ) as count FROM table

I assume your example is a truncated version of your actual query, so perhaps you should post what you are after to get a, possibly, more optimal query.

EDIT

Working directly from my brain, something like this should be more optimal.

SELECT p.PostPID, p.PostUID, p.PostText, p.PostTime, u.UserUID, u.UserName, u.UserImage, u.UserRep, COUNT(v.FlagTime) as postFlags
    FROM Flags as f 
    JOIN Posts as p ON p.PostPID = f.FlagPID
    JOIN Users AS u ON p.PostUID = u.UserUID
LIMIT 0, 30
GROUP BY p.PostPID
ORDER BY PostTime DESC