Question

我有一个MySQL问题。

我有两张桌子：公司＆amp;产品

现在我需要在Company表中选择行并计算每个公司的产品数量。

以下是一个例子：

Company:
---------------
| id   | Name |
---------------
| 1    | c1   |
| 2    | c2   |
| 3    | c3   |
| 4    | c4   |
---------------

Products:
--------------------
| id   | companyid |
--------------------
| 1    | 3         |
| 2    | 1         |
| 3    | 4         |
| 4    | 3         |
| 5    | 2         |
--------------------

我需要得到的结果是：

----------------------------
| id   | Name | numproducts|
----------------------------
| 1    | c1   |  1         |
| 2    | c2   |  1         |
| 3    | c3   |  2         |
| 4    | c4   |  1         |
----------------------------

很抱歉，如果问题是基本的。提前谢谢。

Answer 1

你可以使用分组和计数来得到你的答案

select 
  c.id, c.name, count(*) as numproducts 
from
  company c join products p on c.id = p.companyid 
group by 
  c.id, c.name

Answer 2

加入2个表，然后按公司表中所需的字段进行分组：

SELECT
      c.name
    , COUNT(p.id) AS no_of_products
FROM company c
      INNER JOIN products p
                  ON c.id = p.companyid
GROUP BY
      c.name

Answer 3

您可以使用此查询

SELECT * , 
     (SELECT COUNT( 1 ) 
           FROM products p2 WHERE p2.companyid = p1.id) AS no_of_records
FROM `company` p1

计算连接到其他表的行数

3 个答案: