如何使用组和多个连接进行查询

Question

你好，我需要了解一下。我有 3 个表：

产品

id_product	name
1	car
2	plane
3	bike

数量

id_product	quantity
1	10
2	17
3	5

价格

id_product	id_group	price
1	1	5.00
1	2	6.00
1	3	7.00
2	1	10.00
2	2	11.00
2	3	12.00
3	1	20.00
3	2	21.00
3	3	22.00

通过查询我希望得到这样的结果：

name	price1	price2	price3	quantity
car	5.00	6.00	7.00	10
plane	10.00	11.00	12.00	17
bike	20.00	21.00	22.00	5

我不能以这个结果为目标我的查询是：

    SELECT
product.name,price.price,quantity.quantity
FROM product

LEFT JOIN price
ON product.id_product = price.id_product
WHERE price.id_group = 1
LEFT JOIN price
ON product.id_product = price.id_product
WHERE price.id_group = 2
LEFT JOIN price
ON product.id_product = price.id_product
WHERE price.id_group = 3

LEFT JOIN quantity
ON product.id_product = quantity.id_product

Answer 1

首先，在tableprice中使用条件聚合获取价格，然后加入：

SELECT p.name, t.price1, t.price2, t.price3, q.quantity
FROM products p
LEFT JOIN quantity q ON q.id_product = p.id_product
LEFT JOIN (
  SELECT id_product,
         MAX(CASE WHEN id_group = 1 THEN price END) price1,
         MAX(CASE WHEN id_group = 2 THEN price END) price2,
         MAX(CASE WHEN id_group = 3 THEN price END) price3
  FROM price
  GROUP BY id_product
) t ON t.id_product = p.id_product

如何使用组和多个连接进行查询

how to make query with group and multiple joins

mysql

join

left-join

where-clause

prestashop-1.6