两个不同组中具有不同列值的记录数答案

【问题标题】：Number of records with different column values across two different groups两个不同组中具有不同列值的记录数
【发布时间】：2021-12-21 20:09:42
【问题描述】：

我在 postgresql 中有下表，我们称之为table1

entity id	entity group	value
1	A	5000
2	A	4000
3	A	3000
4	A	2000
5	A	1000
1	B	5000
2	B	4800
3	B	2700

我需要找出在不同实体组中具有不同值的实体的数量。
在上面的示例中，答案将是 2 (entity_id: 2,3)。

我有一个 hacky 方法如下

with entity_diff as (
    with entitya as (
        select entity_id,
               value as value_group_a
        from table1
        where entity_group = 'A'
    ),
         entityb as (
             select entity_id,
                    value as value_group_b
             from table1
             where entity_group = 'B'
         )
    select entitya.entity_id,
           entitya.value_group_a - entityb.value_group_b as value_diff
    from entitya
             inner join entityb on entitya.entity_id = entityb.entity_id
)
select count(*) from from entity_diff
where abs(entity_diff.value_diff) > 0;

有没有更简单的方法来获得这个答案，当我需要比较 3 或 4 个组时也可以扩展。

【问题讨论】：

标签： sql postgresql group-by

【解决方案1】：

您可以将count(distinct) 与子查询一起使用：

select count(*) from (select t1.id, count(distinct t1.value) h from table1 t1 group by t1.id) t2 
where t2.h = (select count(*) from table1 t3 where t3.id = t2.id) and t2.h > 1;

输出：

count
-----
2

而对应的实体ID为(select t2.id from ...)：

id
-----
2
3

【讨论】：

【解决方案2】：

您可以尝试以下使用方法：

带有从句的分组
在相似的entity_ids 上自我加入，但不同的entitygroups 具有不同的值。

查询 #1

select 
    count(1)
from (
    select
        entityid
    from
        table1
    group by
        entityid
    having
        count(distinct entitygroup) > 1 and
        min(value) <> max(value)
) t1;

count
2

查询 #2

select
    entityid
from
    table1
group by
    entityid
having
    count(distinct entitygroup) > 1 and
    min(value) <> max(value);

entityid
2
3

查询 #3

select
    count(distinct t1.entityid)
from
    table1 t1
inner join
    table1 t2 on t1.entityid = t2.entityid and
                 t1.entitygroup < t2.entitygroup and
                 t1.value <> t2.value;

count
2

查询 #4

select
    count(distinct t1.entityid)
from
    table1 t1
inner join
    table1 t2 on t1.entityid = t2.entityid and
                 t1.entitygroup < t2.entitygroup and
                 abs(t1.value - t2.value)>0;

count
2

查询 #5

select distinct
    t1.entityid
from
    table1 t1
inner join
    table1 t2 on t1.entityid = t2.entityid and
                 t1.entitygroup < t2.entitygroup and
                 abs(t1.value - t2.value) > 0;

entityid
2
3

View working demo on DB Fiddle

【讨论】：