PostgreSQL 9.3：在数据透视表查询中过滤

Question

我有这些记录：

  Employee_Number    Employee_role         Group_Name
  ----------------------------------------------------
  EMP101             C# Developer            Group_1      
  EMP102             ASP Developer           Group_1      
  EMP103             SQL Developer           Group_2      
  EMP104             PLSQL Developer         Group_2      
  EMP101             Java Developer          
  EMP102             Web Developer          
  EMP101             DBA          
  EMP105             DBA          
  EMP106             SQL Developer           Group_3      
  EMP107             Oracle Developer        Group_3      
  EMP101             Oracle Developer        Group_3      

希望以下列格式显示上述记录的数据透视表：

 Employee_Number     TotalRoles      TotalGroups       Available     Others     Group_1     Group_2      Group_3
 -----------------------------------------------------------------------------------------------------------------
 EMP101                   4               3                2            2          1                        1
 EMP102                   2               3                1            1          1 
 EMP103                   1               3                1            0                      1
 EMP104                   1               3                1            0                      1
 EMP105                   1               3                0            1
 EMP106                   1               3                1            0                                   1
 EMP107                   1               3                1            0                                   1

对于上述结果，我使用以下脚本：

SELECT * FROM crosstab(
      $$SELECT grp.*, e.group_name
         , CASE WHEN e.employee_number IS NULL THEN 0 ELSE 1 END AS val
    FROM  (
       SELECT employee_number
        , count(employee_role)::int            AS total_roles
        , (SELECT count(DISTINCT group_name)::int
           FROM   employee
           WHERE  group_name <> '')            AS total_groups
        , count(group_name <> '' OR NULL)::INT AS available                    
        , count(group_name =  '' OR NULL)::int AS others
       FROM   employee
       GROUP  BY employee_number
       ) grp
    LEFT   JOIN employee e ON e.employee_number = grp.employee_number
                  AND e.group_name <> ''         
    ORDER  BY grp.employee_number, e.group_name$$
     ,$$VALUES ('Group_1'),('Group_2'),('Group_3')$$
   ) AS ct (employee_number text
      , total_roles  int
      , total_groups int
      , available    int
      , others       int
      , "Group_1"    int
      , "Group_2"    int
      , "Group_3"    int);

但是：现在我想通过过滤 Group_Name 来显示上述记录的数据透视表。 这意味着如果我想显示唯一 Group_Name= Group_3 的数据透视表，那么它有 仅显示仅属于 Group_Name= Group_3 的员工。

如果我只想查看属于 Group_3 的员工，而不是它必须显示给我：

   Employee_Number    total_roles  total_groups   available    others    Group_3
  ------------------------------------------------------------------------------- 
       EMP106             1             3            1            0            1
       EMP107             1             3            1            0            1

注意：正如您在第一张表中看到的，员工 EMP106 和 EMP107 仅属于 到Group_Name = Group_3。员工EMP101 也属于但他也属于其他组 所以不应出现在此表中。

Answer 1

如何排除违规行：

• Select rows which are not present in other table

crosstab() 查询已改编：

SELECT * FROM crosstab(
    $$SELECT grp.*, e.group_name
           , CASE WHEN e.employee_number IS NULL THEN 0 ELSE 1 END AS val
      FROM  (
         SELECT employee_number
              , count(employee_role)::int            AS total_roles
              , (SELECT count(DISTINCT group_name)::int
                 FROM   employee
                 WHERE  group_name <> '')            AS total_groups
              , count(group_name <> '' OR NULL)::int AS available
              , count(group_name = '' OR NULL)::int  AS others
         FROM   employee
         GROUP  BY employee_number
         ) grp
      JOIN   employee e USING (employee_number)
      WHERE  e.group_name = 'Group_3'
      AND    NOT EXISTS (
         SELECT 1 FROM employee
         WHERE  employee_number = e.employee_number
         AND    group_name  e.group_name
         )
      ORDER  BY employee_number$$
   ,$$VALUES ('Group_3')$$
   ) AS ct (employee_number text
      , total_roles  int
      , total_groups int
      , available    int
      , others       int
      , "Group_3"    int);

但正如您所见，我们在这里根本不需要crosstab()。简化为：

SELECT grp.*, 1 AS "Group_3"
FROM  (
   SELECT employee_number
        , count(employee_role)::int            AS total_roles
        , (SELECT count(DISTINCT group_name)::int
           FROM   employee
           WHERE  group_name <> '')            AS total_groups
        , count(group_name <> '' OR NULL)::int AS available
        , count(group_name = '' OR NULL)::int  AS others
   FROM   employee
   GROUP  BY employee_number
   ) grp
JOIN   employee e USING (employee_number)
WHERE  e.group_name = 'Group_3'
AND    NOT EXISTS (
   SELECT 1 FROM employee
   WHERE  employee_number = e.employee_number
   AND    group_name <> e.group_name
   )
ORDER  BY employee_number;

"Group_3" 列在这里实际上只是噪音，因为根据定义，它始终是 1。

如果以这种方式只选择了一小部分行，那么这个带有LATERAL 连接的版本应该会更快：

SELECT e.employee_number
     , grp.total_roles
     , total.total_groups
     , grp.available
     , grp.others
     , 1 AS "Group_3"
FROM  (
   SELECT employee_number
   FROM   employee e
   WHERE  group_name = 'Group_3'
   AND    NOT EXISTS (
      SELECT 1 FROM employee
      WHERE  employee_number = e.employee_number
      AND    group_name <> e.group_name
      )
   ) e
, LATERAL (
   SELECT count(employee_role)::int            AS total_roles
        , count(group_name <> '' OR NULL)::int AS available
        , count(group_name = '' OR NULL)::int  AS others
   FROM   employee
   WHERE  employee_number = e.employee_number
   GROUP  BY employee_number
   ) grp
,    (
   SELECT count(DISTINCT group_name)::int AS total_groups
   FROM   employee
   WHERE  group_name <> ''
   ) total
ORDER  BY employee_number;

LATERAL 解决方案和性能的详细信息：

• Optimize GROUP BY query to retrieve latest row per user

适用于任何组的简单通用解决方案

未针对性能进行优化，但易于适应：

<original crosstab query from your question>
WHERE  "Group_3" = 1
AND    "Group_1" IS NULL
AND    "Group_2" IS NULL
AND    "Group_4" IS NULL
AND    others = 0  -- to rule out membership in the "empty" group
-- possibly more ...