Question

我有一张表，其中包含大量花费的小时数。我试图根据日期的特定特征获得花费的小时数。我的查询将与此任务竞争，但如果某个特定日期的特定特征集没有值，则该日期不会返回任何数据。我知道如果我用不同的连接类型加入表时如何解决这个问题，但是当连接在where语句中时我不知道如何做到这一点。

SELECT
t1.dates,
t1.hours1,
t2.hours2,
t3.hours3,
t4.hours4

FROM 
    (
        SELECT
        dates,
        SUM(times) AS hours1
        FROM mytable
        WHERE
        characterisics1
        GROUP By dates
    ) t1,
    (
        SELECT
        dates,
        SUM(times) AS hours2
        FROM mytable
        WHERE
        characterisics2
        GROUP By dates
    ) t2,
    (
        SELECT
        dates,
        SUM(times) AS hours3
        FROM mytable
        WHERE
        characterisics3
        GROUP By dates
    ) t3,
    (
        SELECT
        dates,
        SUM(times) AS hours4
        FROM mytable
        WHERE
        characterisics4
        GROUP By dates
    ) t4

WHERE
t1.dates = t2.dates and t1.dates = t3.dates and t1.dates = t4.dates

ORDER BY
t1.dates DESC

Answer 1

使用条件聚合。。。这么简单：

SELECT dates,
       SUM(CASE WHEN characterisics1 THEN times ELSE 0 END) AS hours1,
       SUM(CASE WHEN characterisics2 THEN times ELSE 0 END) AS hours2,
       SUM(CASE WHEN characterisics3 THEN times ELSE 0 END) AS hours3,
       SUM(CASE WHEN characterisics4 THEN times ELSE 0 END) AS hours4,
       SUM(CASE WHEN characterisics5 THEN times ELSE 0 END) AS hours5
FROM mytable
GROUP By dates;

加入子查询和丢失数据

1 个答案: