Question

以下是我的两张桌子;我希望结果如第三个表所示。我怎么能在MySQL中这样做（假设FULL JOIN）？

table_sales

product_id    quantity    date
c001          20        2013-09-03
t008          30        2013-09-01
t008          20        2013-09-03
c001          90        2013-09-09

table_returns

product_id    quantity    date
t008          40        2013-09-08
t008          30        2013-09-01
c001          10        2013-09-03

我希望获得如下结果：

product_id     sale_qty      return_qty        date
c001           20            10              2013-09-03
c001           90            -               2013-09-09
t008           30            30              2013-09-01
t008           20            -               2013-09-01
t008           -             40              2013-09-08

Answer 1

我执行full join的首选方法是获取所有ID的列表以及left join到该列表：

select driver.product_id, s.quantity as sale_qty, r.quantity as return_qty, driver.date
from (select product_id, date from table_sales
      union 
      select product_id, date from table_returns
     ) driver left join
     table_sales s
     on driver.product_id = s.product_id and driver.date = s.date left join
     table_returns r
     on driver.product_id = r.product_id and driver.date = r.date;

我发现将union放在from子句中会使查询更方便。关于处理变量，公式和连接的逻辑只需要包含一次。

Here是证明它有效的SQL小提琴。

Answer 2

MySQL缺乏对FULL OUTER JOIN的支持。

因此，如果您想在MySQL上模拟完全加入，请查看here。

这是一个非常有用的链接，描述了完整连接的解决方法

示例解决方法将类似于

SELECT  t_13.value AS val13, t_17.value AS val17
FROM    t_13
LEFT JOIN
t_17
ON      t_13.value = t_17.value
UNION ALL
SELECT  t_13.value AS val13, t_17.value AS val17
FROM    t_13
RIGHT JOIN
t_17
ON      t_13.value = t_17.value
WHERE   t_13.value IS NULL
ORDER BY
COALESCE(val13, val17)
LIMIT 30

什么是正确的MySql FULL JOIN语法？

2 个答案: