SQL（mysql）排序表并获取其在排序表中的位置的行？

Question

Basically I have this table:

Table QID, UID, system, added(unix timestamp), errors

What Im trying to do is to select a row via UID, But before that sort the table by 'added' so its in timestamps DESC order and then get the single row with its position in the sorted table.

I currently have this which does rank the rows, but how would I get the single row from it:

SET @rank=0;
SELECT @rank := @rank +1 AS rank, UID
FROM table
GROUP BY UID
ORDER BY added DESC

Answer 1

You would use a subquery:

SELECT *
FROM (SELECT @rank := @rank +1 AS rank, UID, added
      FROM (SELECT UID, added
            FROM t cross join
                   (SELECT @rank := 0) var
            GROUP BY UID
            ORDER BY added ASC
           ) t
     ) t
WHERE UID = 12346;

One problem is that added is indeterminate when there are multiple rows for a given UID . I suspect that you want MAX(added) instead.

Answer 2

You can either do something along the lines of:

SELECT COUNT(*)+1 AS rank FROM table
WHERE added < (SELECT added FROM table WHERE UID=123)

Or maybe this:

SELECT * FROM (
    SELECT @rank := @rank+1 AS rank, UID
    FROM table
    GROUP BY UID
    ORDER BY added ASC
) tmp WHERE UID=123