Question

我有一张桌子：device

----------------------------------------------------------------
| device__some_id   |   device__os_name  |  device__os_version |
 ---------------------------------------------------------------
|       0                   android               3.0            |

|       0                   android               3.0            |

|       0                   android               4.0            |

|       1                   ios                   8.0            |

|________________________________________________________________|

我有一个查询，它为每个租户返回count(*)，os_name，os_version组合。输出：

--------------------------------------------------------------------------
| device__some_id   |   device__os_name  |  device__os_version | Count |
 -------------------------------------------------------------------------
        0                    android               3.0               2
        0                    android               4.0               1
        1                    ios                   8.0               1

使用的查询：

SELECT f,p,q,count (*)
FROM (SELECT  device__some_id as f, device__os_name as p, device__os_version as q FROM device) as foo
GROUP BY f,p,q

问题：

我有另一张表dim_os，其中包含以下字段：

 | dim_os__some_id   |   dim_os__os_type  |  dim_os__os_version |
     ------------------------------------------------------------
            1                 android               3.0               
            2                 android               4.0              
            3                 ios                   8.0

我想要做的只是用device_os_name表中的device_os_version替换第一个查询输出中some_id和dim_os的每个出现。

我的尝试：

SELECT f, p, count (*)
FROM (SELECT  dev.device__some_id as f, j2.dim_os__some_id as p  FROM device AS dev 
INNER JOIN dim_os as j1 ON dev.device__os_name = j1.dim_os__os_type 
INNER JOIN dim_os as j2 ON dev.device__os_version = j2.dim_os__os_version) as foo
GROUP BY f,p ;

没有给我正确的计数。我哪里错了？

Answer 1

嗯，不知道你为什么要做两个内连接，我会尝试一个（有两个条件）。

但我并不完全确定我理解你想要的输出！

无论如何：

SELECT f, p, count (*)
FROM 
     (SELECT  
       dev.device__some_id as f, 
       j1.dim_os__some_id as p  
      FROM device AS dev 
      INNER JOIN dim_os as j1 
          ON dev.device__os_name = j1.dim_os__os_type and                
             dev.device__os_version = j1.dim_os__os_version) as foo
GROUP BY f,p ;

请参阅SqlFiddle

Postgres - 基于多列的Count（）

1 个答案: