如果项目已排序,我可以运行select语句并获取行号吗?
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 | |
+-------------+---------------------+------+-----+---------+----------------+
然后我可以运行此查询以按ID获取订单数量:
SELECT itemID, COUNT(*) as ordercount
FROM orders
GROUP BY itemID ORDER BY ordercount DESC;
这给了我表中每个itemID
的计数,如下所示:
+--------+------------+
| itemID | ordercount |
+--------+------------+
| 388 | 3 |
| 234 | 2 |
| 3432 | 1 |
| 693 | 1 |
| 3459 | 1 |
+--------+------------+
我想得到行号,所以我可以说itemID=388
是第一行,234
是第二行等(基本上是订单的排名,而不仅仅是原始计数)。我知道当我得到结果集时,我可以在Java中执行此操作,但我想知道是否有一种方法可以纯粹在SQL中处理它。
更新
设置等级会将其添加到结果集中,但未正确排序:
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this。
将您的查询更改为:
SET @rank=0;
SELECT @rank:=@rank+1 AS rank, itemID, COUNT(*) as ordercount
FROM orders
GROUP BY itemID
ORDER BY ordercount DESC;
SELECT @rank;
最后一个选择是你的计数。
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的解决方案有效,但是通过利用table.*
语法,我们可以avoid repeating内部select
的列名称,并获得更简单/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;
您可以使用MySQL变量来执行此操作。这样的东西应该工作(但是,它包含两个查询)。
SELECT 0 INTO @x;
SELECT itemID,
COUNT(*) AS ordercount,
(@x:=@x+1) AS rownumber
FROM orders
GROUP BY itemID
ORDER BY ordercount DESC;