Question

我有一张这样的表

id userid    game   date_t       hdigit   inside  outside
1  user101    xy     02-09-2017    1       10
2  user101    xy     02-09-2017    1               40
3  user101    xx     02-09-2017    2       40
4  user101    xx     02-09-2017    3               90

我想要显示数据，如

id userid    game   date_t     hdigit inside outside
1  user101    xy    02-09-2017  1       10     40
3  user101    xx    02-09-2017  2       40
4  user101    xx    02-09-2017  3              90

我试过这个

SELECT h.userid,h.game,h.date_t,h.hdigit,h.inside,htwo.outside 
 FROM `hadap_game` AS h JOIN hadap_game AS htwo WHERE h.userid=:user
 AND htwo.userid=:uer AND h.hdigit=htwo.hdigit AND h.game=htwo.game 
 AND h.inside IS NOT NULL AND htwo.outside IS NOT NULL

它打印上面的东西，但我想要打印具有空值的行

Answer 1

我认为你可以简单地使用GROUP BY吗？

SELECT 
    h.userid,
    h.game,
    h.date_t,
    h.hdigit,
    MAX(IFNULL(h.inside, htwo.inside)) AS inside,
    MAX(IFNULL(h.outside, htwo.outside)) AS outside
 FROM 
    hadap_game AS h 
    LEFT JOIN hadap_game AS htwo ON htwo.userid = h.userid AND htwo.hdigit = h.hdigit AND htwo.game = h.game AND htwo.id <> h.id
WHERE 
    h.userid = :user
GROUP BY
    h.userid,
    h.game,
    h.date_t,
    h.hdigit;

这会做一些你可能不需要/想要的其他事情，但它与原始查询基本相同，除了它在每个唯一引用没有两行时起作用。

Answer 2

假设只有1或2行（所以不是3个或更多匹配的行）： -

SELECT h.userid,
h.game,
h.date_t,
h.hdigit,
COALESCE(h.inside,h2.inside) AS inside,
COALESCE(h.outside,h2.outside) AS outside
FROM `hadap_game` AS h 
LEFT OUTER JOIN hadap_game AS h2 
ON h.hdigit=h2.hdigit 
AND h.game=h2.game 
WHERE h.userid=:user
AND h2.userid=:uer 
UNION
SELECT h2.userid,
h2.game,
h2.date_t,
h2.hdigit,
COALESCE(h.inside,h2.inside) AS inside,
COALESCE(h.outside,h2.outside) AS outside
FROM `hadap_game` AS h2
LEFT OUTER JOIN hadap_game AS h 
ON h.hdigit=h2.hdigit 
AND h.game=h2.game 
WHERE h.userid=:user2
AND h2.userid=:uer2

加入同一个表，忽略空值

2 个答案: