计算子查询中的行数

2022-01-23 00:00:00 sql subquery mysql

如何将 SELECT 查询中的行数计为值?比如

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

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

所以该计数是子查询 SELECT * FROM anothertable 返回的行数的整数.

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

编辑

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

推荐答案

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

我假设您的示例是实际查询的截断版本，因此也许您应该发布您所追求的内容以获得可能更优化的查询.

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.

编辑

直接从我的大脑中工作，这样的事情应该更理想.

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

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