SQL一起计数行

Question

id  partner_id  date_created    status  item_id
3   2   1322861013  redirected  1
4   2   1322943245  redirected  6
5   3   1322943246  redirected  6
6   2   1322943247  redirected  6

如何计算存在相同item_id的行数？ 表名是orders

以上示例我希望它输出：

There's 3 rows with the item_id 6
There's 1 rows with the item_id 1

我只知道如何通过一些php循环来做些复杂的事情

Answer 1

这里使用的模式是COUNT()与GROUP BY结合使用：

SELECT item_id, COUNT(id) AS item_count FROM orders GROUP BY item_id

您将获得两列，可以根据需要轻松地重新设置其格式。

Answer 2

mysql> create table test(
    ->        row integer
    -> ) ;
Query OK, 0 rows affected (0.05 sec)

mysql> insert into test values ( 3 ) , ( 3 ) , ( 3 ) , ( 1 ) ;
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select count(*) from test group by row;
+----------+
| count(*) |
+----------+
|        1 |
|        3 |
+----------+
2 rows in set (0.03 sec)

mysql>

Answer 3

SELECT item_id, COUNT(id) FROM orders 
GROUP BY item_id