MySql完全联接(联合)和对多个日期列的排序 [英] MySql full join (union) and ordering on multiple date columns

问题描述

一个相当复杂的sql查询，可能会使我变得更加困难: 我有两个桌子:

A rather complicated sql query that I might be making much more difficult that it should be: I have two tables:

新闻: 新闻ID，日期时间，新闻文本

News: newsid, datetime, newstext

图片: pictureid，日期时间，imgPath

Picture: pictureid, datetime, imgPath

两者没有关系，我只是在新闻/图片创建的日期之前加入

The two are not related, I am only joining by the date that the news/picture was created on

SQL:

SELECT * FROM news as n LEFT OUTER JOIN (SELECT count(pictureid), datetime 
FROM picture GROUP BY DATE(datetime)) as p ON DATE(n.datetime) = DATE(p.datetime) 
UNION 
SELECT * FROM news as n RIGHT OUTER JOIN (SELECT count(pictureid), 
datetime FROM picture GROUP BY DATE(datetime)) as p ON 
DATE(n.datetime) = DATE(p.datetime) 

我必须使用union来模拟MySQL中的完整外部联接. 结果:

I have to use union to simulate a full outer join in MySQL. The results:

newsid     text     datetime  count()   datetime 
1       sometext   2011-01-16   1       2011-01-16 
2         moo2    2011-01-19  NULL        NULL 
3        mooo3    2011-01-19  NULL        NULL 
NULL      NULL      NULL       4         2011-01-14 

问题是，我显然以两个日期列结尾-一个来自新闻，一个来自图片，这意味着我无法按日期排序，并按正确的顺序排序！有任何想法吗?即使这意味着要重组数据库！我需要将日期放在一栏中.

The problem being that I obviously end up with two date columns- one from news and one from pictures, this means i cannot order by date and have it be in the correct order! Any ideas? Even if it means restructuring the database! I need date to be in a single column.

答案来自SeRPRo 完整的工作代码为:

The answer came from SeRPRo The completed working code is:

SELECT `newsid`, `text`,
    CASE 
    WHEN `datetime` IS NULL 
    THEN `pdate` 
    ELSE `datetime` 
    END 
    as `datetime`, 

`pcount` FROM 
(
    (SELECT * FROM news as n LEFT OUTER JOIN 
        (SELECT count(pictureid) as pcount, datetime as pdate FROM picture GROUP BY DATE(datetime)) as p 
        ON DATE(n.datetime) = DATE(p.pdate) ORDER BY datetime
    )
    UNION
    (SELECT * FROM news as n RIGHT OUTER JOIN 
        (SELECT count(pictureid) as pcount, datetime as pdate FROM picture GROUP BY DATE(datetime)) as p 
        ON DATE(n.datetime) = DATE(p.pdate) ORDER BY datetime
    ) 

) as x
ORDER BY datetime

推荐答案

仅使用您的数据库结构和查询，并且由于FULL OUTER JOIN在MySQL中不可用，所以我认为一个解决方案可能是:

just using your database structure and your query, and since FULL OUTER JOIN is not available in MySQL, I think a solution could be this:

SELECT
    `newsid`,
    `text`,
    CASE
        WHEN `datetime` IS NULL THEN `pdate`
        ELSE `datetime`
    END as `datetime,
    `pcount`
(
SELECT *
FROM `news` as `n`
    LEFT OUTER JOIN (
                        SELECT count(pictureid) as `pcount`, datetime as `pdate`
                        FROM picture GROUP BY DATE(datetime)
                    ) as p ON DATE(n.datetime) = DATE(p.datetime) 
    UNION
SELECT * 
    FROM `news` as `n`
    RIGHT OUTER JOIN (
                        SELECT count(pictureid) as `pcount`, datetime as `pdate`
                        FROM picture GROUP BY DATE(datetime)
                    ) as p ON DATE(n.datetime) = DATE(p.datetime) 

)

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