Sql GROUP BY未按预期工作

这是我的样本表，只有一点信息

select * from juniper_fpc';       
    id     |  router   |     part_name      
-----------+-----------+--------------------
 722830939 | BBBB-ZZZ1 | MPC-3D-16XGE-SFPP 
 722830940 | BBBB-ZZZ1 | MPC-3D-16XGE-SFPP 
 723103163 | AAAA-ZZZ1 | DPCE-R-40GE-SFP   
 723103164 | AAAA-ZZZ1 | MPC-3D-16XGE-SFPP 
 723103172 | AAAA-ZZZ1 | DPCE-R-40GE-SFP   
 722830941 | BBBB-ZZZ1 | MPC-3D-16XGE-SFPP

我要做的是从router列中识别只有part_名称条目以MPC开头的元素。我想到的是这个，但它是错误的，因为它列出了上述两个元素

SELECT   router
FROM     juniper_fpc
WHERE    part_name LIKE 'MPC%'
GROUP BY router
ORDER BY router;
  router   
-----------
 AAAA-ZZZ1
 BBBB-ZZZ1

---

如果您的意思是只选择那些路由器，它们的所有部件名称都以MPC开头，那么您的查询应该是：

SELECT   s.router
FROM     juniper_fpc s
WHERE    NOT EXISTS(select distinct id from juniper_fpc t
                    where t.id = s.id part_name NOT LIKE 'MPC%')
GROUP BY s.router
ORDER BY s.router;

---

如果您的意思是只选择那些路由器，它们的所有部件名称都以MPC开头，那么您的查询应该是：

SELECT   s.router
FROM     juniper_fpc s
WHERE    NOT EXISTS(select distinct id from juniper_fpc t
                    where t.id = s.id part_name NOT LIKE 'MPC%')
GROUP BY s.router
ORDER BY s.router;

---

假设您想要的路由器只有部分名称，如“MPC%”，则可以使用条件计数：

select * from (
  select router, 
    count(case when part_name like 'MPC%' then 1 else null end) as cnt_mpc,
    count(*) as cnt_overall
  from juniper_fpc  
  group by router) v_inner
where cnt_mpc = cnt_overall

这可以写得更紧凑，尽管可读性稍差

  select router
  from juniper_fpc  
  group by router
  having count(case when part_name like 'MPC%' then 1 else null end)  = count(*) 

---

假设您想要的路由器只有部分名称，如“MPC%”，则可以使用条件计数：

select * from (
  select router, 
    count(case when part_name like 'MPC%' then 1 else null end) as cnt_mpc,
    count(*) as cnt_overall
  from juniper_fpc  
  group by router) v_inner
where cnt_mpc = cnt_overall

这可以写得更紧凑，尽管可读性稍差

  select router
  from juniper_fpc  
  group by router
  having count(case when part_name like 'MPC%' then 1 else null end)  = count(*) 

---

这应该表现良好：

SELECT j1.router
FROM  (
   SELECT   router
   FROM     juniper_fpc
   WHERE    part_name LIKE 'MPC%'
   GROUP    BY router
   ) j1
LEFT   JOIN juniper_fpc j2 ON j2.router = j1.router
                          AND j2.part_name NOT LIKE 'MPC%'
WHERE  j2.router IS NULL
ORDER  BY j1.router;

如果你做得对的话，也不存在可以工作的人：

SELECT router
FROM   juniper_fpc j
WHERE  NOT EXISTS (
   SELECT 1
   FROM   juniper_fpc
   WHERE  router = j.router
   AND    part_name NOT LIKE 'MPC%'
   )
GROUP  BY router
ORDER  BY router; 

详情：

或者，使用Postgres 9.4或更高版本的语法：

SELECT router
FROM   juniper_fpc
GROUP  BY router
HAVING count(*) = count(*) FILTER (WHERE part_name LIKE 'MPC%')
ORDER  BY router;

---

最好使用路由器上的索引，每个路由器的部件名。

这应该可以很好地执行：

SELECT j1.router
FROM  (
   SELECT   router
   FROM     juniper_fpc
   WHERE    part_name LIKE 'MPC%'
   GROUP    BY router
   ) j1
LEFT   JOIN juniper_fpc j2 ON j2.router = j1.router
                          AND j2.part_name NOT LIKE 'MPC%'
WHERE  j2.router IS NULL
ORDER  BY j1.router;

如果你做得对的话，也不存在可以工作的人：

SELECT router
FROM   juniper_fpc j
WHERE  NOT EXISTS (
   SELECT 1
   FROM   juniper_fpc
   WHERE  router = j.router
   AND    part_name NOT LIKE 'MPC%'
   )
GROUP  BY router
ORDER  BY router; 

详情：

或者，使用Postgres 9.4或更高版本的语法：

SELECT router
FROM   juniper_fpc
GROUP  BY router
HAVING count(*) = count(*) FILTER (WHERE part_name LIKE 'MPC%')
ORDER  BY router;

---

最好使用路由器上的索引，每个路由器的部件名。

您也可以在此处打开函数：

SELECT
    *
FROM
    (
        SELECT 
            router,
            part_name,
            COUNT(distinct part_name) OVER (PARTITION BY router) as count_of_distinct_parts
        FROM juniper_fpc
    )subqry
WHERE part_name like 'MPC%' AND count_of_distinct_parts = 1

---

如果此查询范围扩大，这将为更复杂的情况打开大门。

您也可以在此处选择窗口功能：

SELECT
    *
FROM
    (
        SELECT 
            router,
            part_name,
            COUNT(distinct part_name) OVER (PARTITION BY router) as count_of_distinct_parts
        FROM juniper_fpc
    )subqry
WHERE part_name like 'MPC%' AND count_of_distinct_parts = 1

---

如果此查询范围扩大，这将为更复杂的情况打开大门。

我看不出您的代码或输出有任何错误，根据u，这两个都应该返回！您的输入数据包含| AAAA-ZZZ1 | MPC-3D-16XGE-SFPP |和| BBBB-ZZZ1 | MPC-3D-16XGE-SFPP |，因此PostgreSQL返回正确的结果。您是否需要只包含部分名称（如“MPC”）而不包含其他名称的记录？也许您希望看到MPC-3D-16XGE-SFPP没有路由器名称“bbbbb-ZZZ1”？在这种情况下，您应该分组并按部件名称排序。我看不出您的代码或输出有任何错误，根据u，这两个都应该返回！您的输入数据包含| AAAA-ZZZ1 | MPC-3D-16XGE-SFPP |和| BBBB-ZZZ1 | MPC-3D-16XGE-SFPP |，因此PostgreSQL返回正确的结果。您是否需要只包含部分名称（如“MPC”）而不包含其他名称的记录？也许您希望看到MPC-3D-16XGE-SFPP没有路由器名称“bbbbb-ZZZ1”？在这种情况下，您应该按部件名称分组和排序。问题：您不能在子查询中引用未聚合的s.id；区别是没有用的；缺少和.问题：无法在子查询中引用未聚合的s.id；区别是没有用的；失踪和失踪。