如何理解用从句计数组中不同值的结果

Question

数据库:版本8.0.26-17 https://www.percona.com/doc/percona-server/8.0/release-notes/Percona-Server-8.0.26-17.html

我有两个问题产生不同的结果。我不明白为什么。

1)

select eev_company_id,
count(distinct maj.dsd_prefix) as maj_cnt,
count(distinct min.dsd_prefix) as min_cnt
from ehev_most_recent as eev
inner join ekohubschema as ehs on  ehs.ehs_subcategory = eev.eev_subcategory
left join datasourcedescription as maj on maj.dsd_prefix = eev.eev_prefix and maj.dsd_type_id = 'MAJ'
left join datasourcedescription as min on min.dsd_prefix = eev.eev_prefix and min.dsd_type_id <> 'MAJ'
where ehs.ehs_category <> 'Exclusionary Factors'
group by eev.eev_company_id
having eev.eev_company_id = 'ADD53604';

结果是：

+----------------+---------+---------+
| eev_company_id | maj_cnt | min_cnt |
+----------------+---------+---------+
| ADD53604       |       2 |       1 |
+----------------+---------+---------+

第二个查询与AND基本相同，但替换了AND。

2)

select 
count(distinct maj.dsd_prefix) as maj_cnt,
count(distinct min.dsd_prefix) as min_cnt
from ehev_most_recent as eev
inner join ekohubschema as ehs on ehs.ehs_subcategory = eev.eev_subcategory
left join datasourcedescription as maj on maj.dsd_prefix = eev.eev_prefix and maj.dsd_type_id = 'MAJ'
left join datasourcedescription as min on min.dsd_prefix = eev.eev_prefix and min.dsd_type_id <> 'MAJ'
where ehs.ehs_category <> 'Exclusionary Factors' AND eev.eev_company_id = 'ADD53604';

此查询的结果是：

+---------+---------+
| maj_cnt | min_cnt |
+---------+---------+
|       2 |       0 |
+---------+---------+

如您所见，这里的min_cnt是0，而对于第一个查询，它是1。差异的原因是什么？

如果删除ekohubschema联接，则得到相同的结果：

select eev_company_id,
count(distinct maj.dsd_prefix) as maj_cnt,
count(distinct min.dsd_prefix) as min_cnt
from ehev_most_recent as eev
left join datasourcedescription as maj on maj.dsd_prefix = eev.eev_prefix and maj.dsd_type_id = 'MAJ'
left join datasourcedescription as min on min.dsd_prefix = eev.eev_prefix and min.dsd_type_id <> 'MAJ'
group by eev.eev_company_id
having eev.eev_company_id = 'ADD53604'; 

+----------------+---------+---------+
| eev_company_id | maj_cnt | min_cnt |
+----------------+---------+---------+
| ADD53604       |       2 |       0 |
+----------------+---------+---------+

ekohubschema表有以下列：ehs_category、ehs_subcategory和ehs_long_description，没有任何公司ID，但它会干扰结果。

我没有看到任何次要的信息源，只有少校。这就是为什么我很难找出计数1(对于min_cnt )来自哪里。

​

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Answer 1

请检查此查询的输出：

select 
   eev_company_id, 
   min.dsd_prefix
from ehev_most_recent as eev
left join datasourcedescription as min on min.dsd_prefix = eev.eev_prefix and min.dsd_type_id <> 'MAJ'
where eev.eev_company_id = 'ADD53604'; 

我认为它(输出)至少包含一次1，如果不是，它就是一个bug。

是的，我认为这是个bug，参见：DBFIDDLE。我在这里报告过：bug 106539

该bug也存在于MariaDB 10.6中，参见：DBFIDDLE