mysql - 连接表并根据值将同一列获取到更多列

Question

假设我连接两个表并得到如下结果

id   vendor vendor_id quantity 
1    Sony          1       25 
1    Apple         2       12  
1    HTC           3        5  

我希望结果是这样的

id Quantity_Sony Quantity_Apple Quantity_HTC
1             25             12            5

我该怎么做，我使用左连接来连接表。我使用mySql

Answer 1

SELECT  ID,
        MAX(CASE WHEN vendor = 'Sony' THEN Quantity END) Quantity_Sony,
        MAX(CASE WHEN vendor = 'Apple' THEN Quantity END) Quantity_Apple,
        MAX(CASE WHEN vendor = 'HTC' THEN Quantity END) Quantity_ATC
FROM
        (
         -- add your existing query here
        ) x
GROUP   BY ID