为具有多个连接的查询编写计数查询答案

【问题标题】：Write count query for a query which has multiple joins为具有多个连接的查询编写计数查询
【发布时间】：2020-04-05 20:37:00
【问题描述】：

对于 Spring JPA，我使用下面的原生查询，我需要实现分页。为此，我需要有一个计数查询，它将返回以下查询返回的行。如何编写计数查询。

SELECT  count(distinct opportunity_vendors.opportunity_id) as oppcount, vendors.name , count(applications.id) as appcount
FROM public.vendors 
  inner join public.opportunity_vendors on vendors.id = opportunity_vendors.vendor_id
  inner join public.opportunities on opportunity_vendors.opportunity_id = opportunities.id
  inner join public.applications on opportunity_vendors.opportunity_id = applications.opportunity_id
  group by vendors.name having length(vendors.name) > 0;```

【问题讨论】：

标签： mysql sql postgresql spring-data-jpa

【解决方案1】：

你可以这样做：

select count(*) from (
SELECT  count(distinct opportunity_vendors.opportunity_id) as oppcount, vendors.name , count(applications.id) as appcount
FROM public.vendors 
  inner join public.opportunity_vendors on vendors.id = opportunity_vendors.vendor_id
  inner join public.opportunities on opportunity_vendors.opportunity_id = opportunities.id
  inner join public.applications on opportunity_vendors.opportunity_id = applications.opportunity_id
  group by vendors.name having length(vendors.name) > 0
) d

最好的问候，
比亚尼

【讨论】：

【解决方案2】：

您可以将查询用作子查询.. 一个简单的方法是

select count(*) 
from (

    SELECT  count(distinct opportunity_vendors.opportunity_id) as oppcount
        , vendors.name 
        , count(applications.id) as appcount
    FROM public.vendors 
      inner join public.opportunity_vendors on vendors.id = opportunity_vendors.vendor_id
      inner join public.opportunities on opportunity_vendors.opportunity_id = opportunities.id
      inner join public.applications on opportunity_vendors.opportunity_id = applications.opportunity_id
      group by vendors.name 
      having length(vendors.name) > 0; 

) t

【讨论】：