Question

我有三个表：

 id | name
----+------
  1 | a
  2 | b
  3 | c
  4 | d

branch_1
 id | parent_id | b1_name
----+-----------+---------
  1 |         1 | aaa
  2 |         1 | bbb
  3 |         1 | ccc
  4 |         2 | ddd
  5 |         2 | eee
  6 |         2 | fff
  7 |         2 | ggg
  8 |         2 | hhh

branch_2
 id | b2_name | parent_id
----+---------+-----------
  1 | b2_aa   |         1
  2 | b2_ba   |         2
  3 | b2_bb   |         2
  4 | b2_bc   |         2

我只想将这些表与唯一值结合使用。我尝试了这段代码：

select p.id, b1.b1_name, b2.b2_name
from parent p
left outer join lateral (select distinct b1.b1_name from branch_1 b1 where b1.parent_id=p.id order by b1.b1_name) as b1 on true
left outer join lateral (select distinct b2.b2_name from branch_2 b2 where b2.parent_id=p.id order by b2.b2_name) as b2 on true

但结果中有重复的值：

 id | b1_name | b2_name
----+---------+---------
  1 | aaa     | b2_aa
  1 | bbb     | b2_aa
  1 | ccc     | b2_aa
  2 | ddd     | b2_ba
  2 | ddd     | b2_bb
  2 | ddd     | b2_bc
  2 | eee     | b2_ba
  2 | eee     | b2_bb
  2 | eee     | b2_bc
  2 | fff     | b2_ba
  2 | fff     | b2_bb
  2 | fff     | b2_bc
  2 | ggg     | b2_ba
  2 | ggg     | b2_bb
  2 | ggg     | b2_bc
  2 | hhh     | b2_ba
  2 | hhh     | b2_bb
  2 | hhh     | b2_bc

我想得到：

 id | b1_name | b2_name
----+---------+---------
  1 | aaa     | b2_aa
  1 | bbb     | ---
  1 | ccc     | ---
  2 | ddd     | b2_ba
  2 | eee     | b2_bb
  2 | fff     | b2_bc
  2 | ggg     | ---
  2 | hhh     | ---

也许看起来很奇怪，但是我只需要唯一的值而不重复。那么，我如何只能拥有唯一的价值？

P.S。我需要一个用于在狮身人面像上进行小平面搜索的表，这样才能正确考虑产品数量，并发出这样的请求：

select * from facetIndex facet b1_name, b2_name

Answer 1

我想知道狮身人面像多值属性是否可以解决这个问题。 they，它们只是整数。因此可以将分支表ID放入MVA（而不是名称）中

如果PostgreSQL拥有group_concat也许可以做到

sql_query = SEELCT p.id, 
    GROUP_CONCAT(DISTINCT b1.id) as b1, 
    GROUP_CONCAT(DISTINCT b2.id) as b2 
FROM parent p 
    LEFT JOIN branch1 b1 ON (b1.parent = p.id) 
    LEFT JOIN branch2 b2 ON (b2.parent = p.id) 
GROUP BY p.id

但是好吗？

...因此，请使用sql_attr_multi功能来运行单独的查询。

sql_query = SELECT id, name FROM parent
sql_attr_multi = uint b1 from query; SELECT parent_id, id FROM branch1 
sql_attr_multi = uint b2 from query; SELECT parent_id, id FROM branch2

这完全在狮身人面像中进行了“连接”。

然后可以直接在MVA上使用，例如SphinxQL查询

select * from facetIndex facet b1 facet b2

Answer 2

您可以使用窗口函数仅在第一行进行外部联接：

select t.id, t.b1_name, b2.b2_name
from (
  select p.id, b1.b1_name, row_number() over (partition by p.id order by b1_name) as rn
  from parent p
    join branch_1 b1 on b1.parent_id = p.id
) t
  left join (
    select parent_id, b2_name, 
           row_number() over (partition by parent_id) as rn
    from branch_2 
  ) b2 on b2.parent_id = t.id and b2.rn = t.rn
order by t.id;

在线示例：https://rextester.com/GNYF31027

如何仅从相关表中选择唯一值

2 个答案: