MySQL – 获取select的行号
我可以运行一个select语句，并获得行号，如果项目sorting？
我有这样一张桌子：
mysql> describe orders; +-------------+---------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+---------------------+------+-----+---------+----------------+ | orderID | bigint(20) unsigned | NO | PRI | NULL | auto_increment | | itemID | bigint(20) unsigned | NO | | NULL | | +-------------+---------------------+------+-----+---------+----------------+ 然后我可以运行这个查询来获取ID的订单数量：
SELECT itemID, COUNT(*) as ordercount FROM orders GROUP BY itemID ORDER BY ordercount DESC;
这给了我这个表中每个itemID的计数：
+--------+------------+ | itemID | ordercount | +--------+------------+ | 388 | 3 | | 234 | 2 | | 3432 | 1 | | 693 | 1 | | 3459 | 1 | +--------+------------+
我也想得到行号，所以我可以告诉itemID=388是第一行， 234是第二行等（本质上是订单的排名，而不仅仅是一个原始计数）。 我知道当我得到结果集的时候，我可以用Java来做到这一点，但是我想知道是否有办法纯粹用SQL来处理它。
更新
设置等级将其添加到结果集中，但没有正确sorting：
mysql> SET @rank=0; Query OK, 0 rows affected (0.00 sec) mysql> SELECT @rank:=@rank+1 AS rank, itemID, COUNT(*) as ordercount -> FROM orders -> GROUP BY itemID ORDER BY rank DESC; +------+--------+------------+ | rank | itemID | ordercount | +------+--------+------------+ | 5 | 3459 | 1 | | 4 | 234 | 2 | | 3 | 693 | 1 | | 2 | 3432 | 1 | | 1 | 388 | 3 | +------+--------+------------+ 5 rows in set (0.00 sec)
看看这个 。
将您的查询改为：
SET @rank=0; SELECT @rank:=@rank+1 AS rank, itemID, COUNT(*) as ordercount FROM orders GROUP BY itemID ORDER BY ordercount DESC;
SELECT @rn:=@rn+1 AS rank, itemID, ordercount FROM ( SELECT itemID, COUNT(*) AS ordercount FROM orders GROUP BY itemID ORDER BY ordercount DESC ) t1, (SELECT @rn:=0) t2;
Swamibebop的解决scheme的工作原理，但通过利用table.*语法，我们可以避免重复内部select的列名，并得到一个更简单/更短的结果：
select @r := @r+1 , z.* from( /* your original select statement goes in here */ )z, (select @r:=0)y;
这样会给你：
select @r := @r+1 , z.* from( select itemID, count(*) as ordercount from orders group by itemID order by ordercount desc )z, (select @r:=0)y;
你可以使用一个mysqlvariables来做到这一点。 像这样的东西应该工作（虽然，这是两个查询）。
SELECT 0 INTO @x; SELECT itemID, COUNT(*) as ordercount, (@x:=@x+1) as rownumber FROM orders GROUP BY itemID ORDER BY ordercount DESC;
