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GroupF
V2EX  ›  MySQL

mysql 5.7 两个临时表 左右连接,同样的临时表 join 连接不上

  •  
  •   GroupF · 2020-11-16 18:21:20 +08:00 · 2501 次点击
    这是一个创建于 1227 天前的主题,其中的信息可能已经有所发展或是发生改变。

    直接能跑的 sql 奉上 ,可能命名不太规范

    左表为主表就出左表,右表为主表出右表

    select * from

    (select DATE_FORMAT(m1, '%Y-%m') as day3 from ( select ('2020-01-23 00:00:00' - INTERVAL DAYOFMONTH('2020-01-23 00:00:00')-1 DAY) +INTERVAL m MONTH as m1 from ( select @rownum:=@rownum+1 as m from (select 1 union select 2 union select 3 union select 4) t1, (select 1 union select 2 union select 3 union select 4) t2, (select 1 union select 2 union select 3 union select 4) t3, (select @rownum:=-1) t0 ) d1 ) d2 where m1<='2020-12-01 00:00:00' order by m1) as datemonths3

    left join (select DATE_FORMAT(m1, '%Y-%m') as day1 from ( select ('2020-01-23 00:00:00' - INTERVAL DAYOFMONTH('2020-01-23 00:00:00')-1 DAY) +INTERVAL m MONTH as m1 from ( select @rownum:=@rownum+1 as m from (select 1 union select 2 union select 3 union select 4) t1, (select 1 union select 2 union select 3 union select 4) t2, (select 1 union select 2 union select 3 union select 4) t3, (select @rownum:=-1) t0 ) d1 ) d2 where m1<='2020-12-01 00:00:00' order by m1) as datemonths2 on datemonths2.day1 = datemonths3.day3

    5 条回复    2020-12-14 13:45:59 +08:00
    mm163
        1
    mm163  
       2020-11-16 19:18:01 +08:00   ❤️ 1
    union
    GroupF
        2
    GroupF  
    OP
       2020-11-17 14:26:13 +08:00
    @mm163 但是 union,完成不了 join 的事情,我固定条数,没有补 0
    GroupF
        3
    GroupF  
    OP
       2020-11-17 14:29:25 +08:00
    再加上条件应该能行,那我就是在表连接以及用函数的时候他们连接,成为新表时候的顺序是怎么
    举个小例子
    select * from
    ((select '2020' as b,'20211' as a ) union
    (select '2021' as b,'20211' ) ) as av
    group by av.a
    GroupF
        4
    GroupF  
    OP
       2020-11-17 14:38:40 +08:00
    仅针对这个例子,我用 having 还是能满足大概
    #分组,a 只能出现一次,但是可能 b 没数据,选有数据的分
    select * from
    ((select '2020' as b,'20221' as a ) union
    (select '2021' as b,'20221' ) ) as av
    group by av.a having (b > 0 or b=0)
    GroupF
        5
    GroupF  
    OP
       2020-12-14 13:45:59 +08:00
    pps,占用大家公共资源了,用相同语句生成的临时表,就不可以 join
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