java - MySQL 设置变量并在同一语句/脚本中运行查询

Question

我有一个数据库客户名称和日期是复合键。我试图在每个日期提取“x”个最大或最小的交易并将其与排名一起插入到另一个表中。

我在单次运行中使用此代码，但当通过 JDBC 从 Java 运行多次时它不起作用。

set @N = 0;

SELECT @N := @N +1 AS rank, name, purchase FROM t1 ORDER BY close purchase
limit 15;

有什么建议吗？

Answer 1

这非常有效:

SELECT t.*, 
       @n := @n + 1 AS rank
  FROM WhateverTable t, (SELECT @n := 0) r

所以你的查询实际上看起来像这样:

SELECT @N := @N +1 AS rank, name, purchase 
FROM t1, (SELECT @N := 0) r 
ORDER BY purchase desc
limit 15;