Question

我对SQL很新，不知道我的查询有什么问题。 PLZ指南

我有2个表产品和product_consumer 1到m关系。我想获得每种产品的所有产品和消费者数量。

这就是我想要的：

id:    pCount
item1, 2
item2, 1

我尝试了以下查询，但它只返回第1条记录/ 1行。

SELECT prd.*, COUNT(pc.id) pCount 
FROM `product` AS prd 
JOIN product_consumer pc ON pc.id = prd.id

Answer 1

试试这个

SELECT pc.id, COUNT(pc.id) pCount 
FROM product AS prd 
JOIN product_consumer pc ON pc.id = prd.id 
GROUP BY pc.id

假设您的架构是这样的：

CREATE TABLE product(
  id int,
  product  varchar(1)
)

CREATE TABLE product_consumer(
  id int,
  consumer  varchar(1),
  pid int
)

如果您想要products所有count的详细信息，则需要在group by clause中包含prd的所有属性，如下所示：

SELECT prd.id, prd.product, count(pc.pid) as pCount  
FROM product AS prd 
JOIN product_consumer pc ON pc.pid = prd.id 
GROUP BY prd.id, prd.product, pc.pid;

请参阅此SQLFiddle

Answer 2

使用GROUP BY条款

SELECT prd.id, count(pc.id) pCount 
FROM product AS prd JOIN product_consumer pc ON pc.id = prd.id
GROUP BY prd.id

Answer 3

实际上，如果您不需要产品名称，则无需加入

SELECT id, count(*)
FROM product_consumer
GROUP BY id;

在进行SQL查询时需要帮助

3 个答案: