加入查询但消除重复

Question

所以我有这些数据，来自 tbl_left :

id   name   type    our_assets
1   'Mira'   cc        10
2   'Mira'   bb        9

还有这个，来自 tbl_right :

id   name   assets_other  name_of_assets
1   'Mira'      3            assets_a
2   'Mira'      1            assets_b
3   'Mira'      1            assets_c
4   'Mira'      1            assets_d

我怎样才能加入两者 table 并得到类似这样的结果：

 name   type    our_assets   assets_other  name_of_assets
'Mira'   cc        10            3            assets_a
'Mira'   bb        9             1            assets_b
'Mira'                           1            assets_c
'Mira'                           1            assets_d

我不在乎列类型和 our_assets 是否具有重复值，我尝试使用 join 但结果变成 8 行而不是 4 行，如：

 name   type    our_assets   assets_other  name_of_assets
'Mira'   cc        10            3            assets_a
'Mira'   cc        10            3            assets_a
'Mira'   bb        9             1            assets_b
'Mira'   bb        9             1            assets_b
'Mira'                           1            assets_c
'Mira'                           1            assets_c
'Mira'                           1            assets_d
'Mira'                           1            assets_d

如果我使用 group by name_of_assets 列类型仅 return "cc" 值。

Answer 1

您需要添加除 name 之外的另一个连接条件，以避免重复记录。一种选择使用 row_number()（在 MySQL 8.0 中可用）：

select r.name, l.type, l.our_assets, r.assets_other, r.name_of_asset
from (select r.*, row_number() over(partition by name order by id) rn from tbl_right) l
left join (select l.*, row_number() over(partition by name order by id) rn from tbl_left) r
    on r.name = l.name and r.rn = l.rn

如果连接两端的记录可能丢失，您可以使用 union all 和聚合代替：

select 
    name,
    max(type) type,
    amx(our_assets) our_assets,
    max(assets_other) assets_other,
    max(name_of_asset) name_of_asset
from (
    select 
        name, 
        type, 
        our_assets, 
        null assets_other, 
        null name_of_asset, 
        row_number() over(partition by name order by id) rn 
    from tbl_left
    union all
    select 
        name, 
        null, 
        null, 
        assets_other, 
        name_of_asset, 
        row_number() over(partition by name order by id) rn 
    from tbl_right
) t
group by name, rn

Answer 2

我想你想 left join 在 id 和 name:

select r.*, l.type, l.our_assets
from tbl_right r left join
     tbl_left l
     on l.id = r.id and l.name = r.name

加入查询但消除重复

Join query but eliminate the duplicate

mysql

sql

join

distinct