mysql - Mysql：一个查询中的“SET @Variable = 0”[Java]

Question

我有两个 sql 查询。但是在Java中我不能设置变量。

我试图将其总结为一个查询。但这不起作用，因为 sql 语法是错误的。

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 部分是你可以做的问题

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

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

Answer 2

你需要像这样加入：

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

如果你有 mysql 8.0，你可以使用：ROW_NUMBER() 或 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);