MySQL：在一个查询中“ SET @Variable = 0” [Java]

Question

我有两个SQL查询。但是在Java中，我无法设置变量。

我试图将其归纳为一个查询。但这不起作用，因为sql语法错误。

SET @rn = 0;
SELECT * 
FROM (SELECT t.id, @rn := @rn + 1 AS rank 
      FROM stats t 
      ORDER BY t.points DESC) t2 
WHERE t2.id = ?;

Answer 1

如果只有SET部分是问题所在

SELECT t.id, @rn := @rn + 1 AS rank 
FROM stats t 
CROSS JOIN ( SELECT @rn := 0 ) as parameters
ORDER BY t.points DESC

您也可以查看本教程http://www.mysqltutorial.org/mysql-row_number/

Answer 2

您需要像这样进行加入：

SELECT stats.id, @rn := @rn+1 AS rank
FROM stats, (SELECT @rn:=0) a
WHERE stats.id = ?

如果您拥有mysql 8.0，则可以使用： ROW_NUMBER() or RANK() ：

SELECT
   id,
   ROW_NUMBER() OVER w AS 'row_number',
   RANK()       OVER w AS 'rank',
FROM stats
WHERE stats.id = ?
WINDOW w AS (ORDER BY points);