SELECT语句中的子查询(MySQL) [英] Subquery in SELECT statement (MySQL)

问题描述

我正在创建一条SQL语句，该语句将返回一个产品列表以及可以在每个商店中找到的每种产品的数量.

I'm creating an SQL statement that will return a list of products and the quantity of each one of them I can find in every store.

我的表的结构(带有一些示例数据)如下:

The structure of my table (with some sample data) is as follows:

productID - size - color - stock - storeID  
1         - S    - RED01 - 1     - BCN   
1         - S    - RED01 - 3     - MAD   
2         - S    - YEL02 - 0     - BCN   
2         - S    - YEL02 - 2     - MAD   
1         - S    - RED01 - 1     - BCN2  

我需要一个与此类似的结果:

I need a result similar to this one:

productID - size - stockBCN (BCN + BCN2) - stockMAD  
1         - S    - 2                     - 3  
2         - S    - 0                     - 2

我正在使用此语句，并且仅适用于独特的产品

I'm using this statement, and works fine just for an unique product

SELECT DISTINCT prodID, size,
    (SELECT SUM(stock) FROM stocks WHERE storeID IN ('BCN','BCN2') AND prodID = 1 AND size = 'S' AND color = 'RED01' GROUP BY prodID, size, color) AS stockBCN,
    (SELECT SUM(stock) FROM stocks WHERE storeID = 'MAD' AND prodID = 1 AND size = 'S' AND color = 'RED01' GROUP BY prodID, size, color) AS stockMAD,
FROM stocks WHERE storeID IN ('BCN','BCN2','MAD')
AND prodID = (1) AND size = 'S' AND color = 'RED01'

如何更改它以使其适用于表中的所有行?

How can I change it to make it work for all the rows in the table?

推荐答案

您可能想利用GROUP BY子句，而不是在那里使用DISTINCT，即:

You probably want to leverage the GROUP BY clause instead of going with DISTINCT there, i.e.:

SELECT productId, Size,
SUM(CASE WHEN storeID IN ('BCN', 'BCN2') THEN stock ELSE 0 END) AS stockBCN,
SUM(CASE WHEN storeID = 'MAD' THEN stock ELSE 0 END) AS stockMAD
FROM stocks
GROUP BY productId, Size

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