SQL 查询 where has children with conditions

Question

假设我有：

a parents table 包含以下列：(id, name)
a children attributes table 包含以下列：(id, child_id, parent_id, 属性, attribute_value)

现在我想过滤掉任何 parent id 的 ，它至少有一个 child 并且：

属性 => intelligence 共 5
属性 => health 共 4

其中一个 child 的 intelligence 为 5，health 为 4，或者一个 child 的 intelligence 为 5，另一个 child 有 health 的 4.

如何在 PostgreSQL 中查询？ 谢谢

Answer 1

如果您只想要 parents 信息：

SELECT 
  DISTINCT parents.id, parents.name 
FROM 
  parents 
  LEFT JOIN attributes ON parents.id = attributes.parent_id 
WHERE 
  (attribute = 'intelligence' AND attribute_value = 5)
   OR (attribute = 'health' AND attribute_value = 4)

Answer 2

首先我们需要加入表 -- 像这样

select p.id as p_id, p.name as parent_name,
       k.* -- we won't need this in later versions
from parent p
join kidatt k on p.id = k.parent_id

现在我们有两个我们关心的属性——让我们进行一个查询来显示那些

select p.id as p_id, p.name as parent_name,
       case when k.attribute = 'intelligence' and k.attribute_value = 5 then 1 else 0 end as has_a1,
       case when k.attribute = 'health' and k.attribute_value = 4 then 1 else 0 end as has_a2
from parent p
join kidatt k on p.id = k.parent_id

我们现在有一个查询，其中每行都有一个 1

现在我们按 parent.

分组

select p.id as p_id, p.name as parent_name,
       SUM(case when k.attribute = 'intelligence' and k.attribute_value = 5 then 1 else 0 end) as has_a1,
       SUM(case when k.attribute = 'health' and k.attribute_value = 4 then 1 else 0 end) as has_a2
from parent p
join kidatt k on p.id = k.parent_id
group by p.id, p.name

现在我们有一个查询，如果一个或多个 child 有 a1 和 a2 大于 0。

现在select结果

select * 
from (
  select p.id as p_id, p.name as parent_name,
       SUM(case when k.attribute = 'intelligence' and k.attribute_value = 5 then 1 else 0 end) as has_a1,
       SUM(case when k.attribute = 'health' and k.attribute_value = 4 then 1 else 0 end) as has_a2
  from parent p
  join kidatt k on p.id = k.parent_id
  group by p.id, p.name
)
where has_a1 > 0 and has_a2 > 0

注意——我写这个查询并不是为了最好的解决这个问题的方法——相反，我写它的方式是向您展示如何在 SQL 中“思考”并通过一系列步骤解决问题。

我必须进行测试才能确定，但我希望这是执行此查询的最快方法（取决于数据和索引等）

select distinct p.id as p_id, p.name as parent_name,          
from parent p
join kidatt k on p.id = k.parent_id
where k.attribute = 'intelligence' and k.attribute_value = 5

intersect

select distinct p.id as p_id, p.name as parent_name,          
from parent p
join kidatt k on p.id = k.parent_id
where k.attribute = 'health' and k.attribute_value = 4

Answer 3

你可以做

的交集

parents children 智力 5
parents children 生命值 4

(SELECT parent_id 
 FROM tab
 WHERE attribute = 'intelligence'
   AND attribute_value = 5       )
INTERSECT
(SELECT parent_id 
 FROM tab
 WHERE attribute = 'health'
   AND attribute_value = 4       )

SQL 查询 where has children with conditions

SQL query where has children with conditions

sql

postgresql