Question

我有以下表格：

人：

person_id   |   name    | 
-------------------------
1           |   John    |
2           |   Adam    |
3           |   Elen    |
-------------------------

订单：

order_id    |   person_id   |   product     | 
---------------------------------------------
1           |       1       |   TV          |
2           |       1       |   Radio       |
3           |       1       |   toothbrush  |
4           |       2       |   mp3 player  |
5           |       2       |   watch       |
6           |       3       |   ps 3        |
---------------------------------------------

现在我需要查询上面的表格以获得以下结果：

person_id   |   name    |   order_count |
-----------------------------------------
1           |   John    |       3       |
2           |   Adam    |       2       |
3           |   Elen    |       1       |
-----------------------------------------

我尝试过类似的事情：

SELECT u.person_id, u.name, COUNT(o.order_id) FROM persons AS p LEFT JOIN orders AS o ON (p.person_id=o.person_id);

不幸的是，这不起作用。你知道如何解决这个问题吗？

Answer 1

select Persons.person_id, Persons.name, p.order_count 
from Persons
inner join (select person_id, count(*) as order_count from Orders group by person_id) p
on Persons.person_id = p.person_id

如果您还需要那些没有任何订单的人，请使用left join代替inner join

Answer 2

尝试这个

SELECT persons.id, persons.name, COUNT(orders.id) AS order_count  FROM orders LEFT JOIN persons ON (persons.person_id=orders.person_id) GROUP BY persons.name

Answer 3

试试这个......

“从tblorders o选择o.person_id，p.name，count（o.person_id）作为order_count 加入tblpersons p on o.person_id = p.person_id 分组由o.person_id，p.name“

Answer 4

试试这个

select o.person_id,p.name,count(o.person_id) as order_count from tblorders o 
Join tblpersons p on o.person_id=p.person_id
group by o.person_id,p.name

Answer 5

select p.person_id, p.name, o.cnt
from Persons p
left join 
(select person_id  , count(order_id) as cnt from Orders group by person_id) o
on p.person_id = o.person_id

获取具有外键的表的记录计数

5 个答案: