如何使用group by获得MySql中的特定部分 - How to get specific part in MySql with group by?

我有一个SQL查询的问题，我将尝试解释我想做什么。这是我的查询，返回一些结果行。

SELECT 
sck.sckid,
sck.prid,
sck.paid,
sck.sckcen,
sum(scd.scdkiek) as count_of_goods,
min(scn.scndat) as `date`
FROM sck 
INNER JOIN scd ON scd.sckid = sck.sckid
INNER JOIN scn ON scn.scnid = scd.scnid
INNER JOIN sandeliai ON sandeliai.paid = sck.paid
WHERE sck.prid = 1376 GROUP BY sckid

这个查询返回结果的"表1":

表1:

sckid    |    prid    |    sckcen    |    count_of_goods    |      date     |
123      |    1376    |    10009     |          0           |   2012-12-31  |
124      |    1376    |    10007     |          15          |   2013-01-25  |
125      |    1376    |    10005     |          0           |   2013-02-13  |
126      |    1376    |    10000     |          18          |   2013-03-15  |

但是我只需要一行所有数据按prid分组，我写了这个查询:

SELECT 
sck.sckid,
sck.prid,
sck.paid,
sck.sckcen,
sum(scd.scdkiek) as count_of_goods,
min(scn.scndat) as `date`
FROM sck 
INNER JOIN scd ON scd.sckid = sck.sckid
INNER JOIN scn ON scn.scnid = scd.scnid
INNER JOIN sandeliai ON sandeliai.paid = sck.paid
WHERE sck.prid = 1376 GROUP BY prid

然后我在表中得到一行数据:

表2:

sckid    |    prid    |    sckcen    |    count_of_goods    |      date     |
123      |    1376    |    10009     |          23          |   2012-12-31  |

这似乎都是正确的，但在date字段中，我需要从表1返回最早的日期，其中count_of_goods> 0，所以我需要这个结果:

表3:

sckid    |    prid    |    sckcen    |    count_of_goods    |      date     |
123      |    1376    |    10009     |          23          |   2013-01-25  |

那么我怎样才能得到表3中的结果呢?

我认为我最初得到的答案可能过于复杂了。假设scd。scdkiek是数字而不是id，那么您可以通过简单地更改INNER JOIN条件来得到您想要的，即

SELECT 
    sck.sckid,
    sck.prid,
    sck.paid,
    sck.sckcen,
    scn.scndat,
    SUM(scd.scdkiek) AS count_of_goods
FROM sck 
INNER JOIN scd 
    ON scd.sckid = sck.sckid
    AND scd.scdkiek > 0
INNER JOIN sandeliai 
    ON sandeliai.paid = sck.paid
INNER JOIN scn 
    ON scn.scnid = scd.scnid
WHERE sck.prid = 1376 
GROUP BY 
    sck.prid

如果做不到这一点，我会考虑使用子查询。子查询将计算每行的count_of_goods。然后，外部查询将使用它来决定是否将该行的日期设置为NULL。MIN(…somedate…，NULL)将返回日期。这反过来意味着您应该获得该行上的count_of_goods不为NULL的最小日期。

子查询按日期分组，因为您正在查找count_of_goods> 0的日期。

这只是一个选择，当然，可能还有其他更有效的方法，但我相信这将达到您的目的

SELECT
    sck.sckid,
    sck.prid,
    sck.paid,
    sck.sckcen,
    SUM(d.count_of_goods) AS count_of_goods,
    MIN(IF(d.count_of_goods>0,d.scndat,NULL)) AS `date`
FROM (
    -- Get the data and group it by date
    SELECT 
        sck.sckid,
        sck.prid,
        sck.paid,
        sck.sckcen,
        scn.scndat,
        SUM(scd.scdkiek) AS count_of_goods
    FROM sck 
    INNER JOIN scd ON scd.sckid = sck.sckid
    INNER JOIN sandeliai ON sandeliai.paid = sck.paid
    INNER JOIN scn ON scn.scnid = scd.scnid
    WHERE sck.prid = 1376 
    GROUP BY 
        sck.prid, -- may not really be needed
        scn.scndat
) AS d
GROUP BY d.prid

尝试使用having，例如

SELECT 
sck.sckid,
sck.prid,
sck.paid,
sck.sckcen,
sum(scd.scdkiek) as count_of_goods,
min(scn.scndat) as `date`
FROM sck 
INNER JOIN scd ON scd.sckid = sck.sckid
INNER JOIN scn ON scn.scnid = scd.scnid
INNER JOIN sandeliai ON sandeliai.paid = sck.paid
WHERE sck.prid = 1376 GROUP BY prid HAVING count_of_goods > 0;

这应该对你有用。这可能会跳过一些行计数= 0，我认为应该是好的(只是我个人的意见)。

请把这作为一个起点，而不是最终的解决方案。

Edit: Updated sum(…)in having with alias

现在我的问题不是很合乎逻辑，我试图在我的问题中结合两个查询，然后我得到一个很好的答案，这是我的解决方案:

SELECT 
sck.sckid,
sck.prid,
sck.paid,
sck.sckcen,
sum(scd.scdkiek) as count_of_goods,
(SELECT 
scn.scndat
FROM sck 
INNER JOIN scd ON scd.sckid = sck.sckid
INNER JOIN scn ON scn.scnid = scd.scnid
WHERE sck.prid = 1376 GROUP BY sck.sckid having sum(scd.scdkiek) > 0 ORDER BY scn.scndat LIMIT 1) as `date`
FROM sck 
INNER JOIN scd ON scd.sckid = sck.sckid
INNER JOIN scn ON scn.scnid = scd.scnid
WHERE sck.prid = 1376 GROUP BY prid;