MySQL - 在选择时获取行号

问题描述

如果项目已排序，我可以运行 select 语句并获取行号吗?

Can I run a select statement and get the row number if the items are sorted?

我有一张这样的桌子:

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:

I can then run this query to get the number of orders by ID:

SELECT itemID, COUNT(*) as ordercount
FROM orders
GROUP BY itemID ORDER BY ordercount DESC;

这给了我表格中每个 itemID 的计数，如下所示:

This gives me a count of each itemID in the table like this:

+--------+------------+
| itemID | ordercount |
+--------+------------+
|    388 |          3 |
|    234 |          2 |
|   3432 |          1 |
|    693 |          1 |
|   3459 |          1 |
+--------+------------+

我也想得到行号，所以我可以知道 itemID=388 是第一行，234 是第二行，等等(本质上是订单，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完全在 SQL 中处理它.

I want to get the row number as well, so I could tell that itemID=388 is the first row, 234 is second, etc (essentially the ranking of the orders, not just a raw count). I know I can do this in Java when I get the result set back, but I was wondering if there was a way to handle it purely in SQL.

更新

设置等级会将其添加到结果集中，但未正确排序:

Setting the rank adds it to the result set, but not properly ordered:

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)

推荐答案

看看这个.

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.

The last select is your count.

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