Oracle PL/SQL之GROUP BY GROUPING SETS

[转自] http://blog.csdn.net/t0nsha/article/details/6538838

使用GROUP BY GROUPING SETS相当于把需要GROUP的集合用UNION ALL联合起来。

当GROUPING SETS里面的分组元素越多时，使用GROUPING SETS比使用UNION ALL性能更好，这可能和使用GROUPING SETS只需要访问一次表有关。

如下两段查询的结果是相等的：

q1（GROUPING SETS）：

SELECT   department_id, job_id, manager_id, AVG (salary)
    FROM employees
GROUP BY GROUPING SETS ((department_id, job_id), (job_id, manager_id));


DEPARTMENT_ID JOB_ID     MANAGER_ID AVG(SALARY)
------------- ---------- ---------- -----------
              SH_CLERK          122        3200
              AC_MGR            101       12000
              ST_MAN            100        7280
              ST_CLERK          121        2675
              SA_REP            148        8650
              SH_CLERK          120        2900
              SH_CLERK          124        2825
              MK_MAN            100       13000
              AD_PRES                     24000
              FI_MGR            101       12000
              SA_REP            146        8500
              SH_CLERK          123        3475
              AD_ASST           101        4400
              IT_PROG           102        9000
              IT_PROG           103        4950
              FI_ACCOUNT        108        7920
              PU_MAN            100       11000
              ST_CLERK          122        2700
              SA_REP            145        8500
              AC_ACCOUNT        205        8300
              AD_VP             100       17000

DEPARTMENT_ID JOB_ID     MANAGER_ID AVG(SALARY)
------------- ---------- ---------- -----------
              ST_CLERK          120        2625
              ST_CLERK          124        2925
              SA_REP            147  7766.66667
              SA_REP            149  8333.33333
              HR_REP            101        6500
              PR_REP            101       10000
              ST_CLERK          123        3000
              SH_CLERK          121        3675
              PU_CLERK          114        2780
              SA_MAN            100       12200
              MK_REP            201        6000
          110 AC_ACCOUNT                   8300
           90 AD_VP                       17000
           50 ST_CLERK                     2785
           80 SA_REP                 8396.55172
           50 ST_MAN                       7280
           80 SA_MAN                      12200
          110 AC_MGR                      12000
           90 AD_PRES                     24000
           60 IT_PROG                      5760
          100 FI_MGR                      12000

DEPARTMENT_ID JOB_ID     MANAGER_ID AVG(SALARY)
------------- ---------- ---------- -----------
           30 PU_CLERK                     2780
           50 SH_CLERK                     3215
           20 MK_MAN                      13000
          100 FI_ACCOUNT                   7920
              SA_REP                       7000
           70 PR_REP                      10000
           30 PU_MAN                      11000
           10 AD_ASST                      4400
           20 MK_REP                       6000
           40 HR_REP                       6500

52 rows selected.

SELECT department_id, job_id, manager_id, AVG (salary) FROM employees GROUP BY GROUPING SETS ((department_id, job_id), (job_id, manager_id)); DEPARTMENT_ID JOB_ID MANAGER_ID AVG(SALARY) ------------- ---------- ---------- ----------- SH_CLERK 122 3200 AC_MGR 101 12000 ST_MAN 100 7280 ST_CLERK 121 2675 SA_REP 148 8650 SH_CLERK 120 2900 SH_CLERK 124 2825 MK_MAN 100 13000 AD_PRES 24000 FI_MGR 101 12000 SA_REP 146 8500 SH_CLERK 123 3475 AD_ASST 101 4400 IT_PROG 102 9000 IT_PROG 103 4950 FI_ACCOUNT 108 7920 PU_MAN 100 11000 ST_CLERK 122 2700 SA_REP 145 8500 AC_ACCOUNT 205 8300 AD_VP 100 17000 DEPARTMENT_ID JOB_ID MANAGER_ID AVG(SALARY) ------------- ---------- ---------- ----------- ST_CLERK 120 2625 ST_CLERK 124 2925 SA_REP 147 7766.66667 SA_REP 149 8333.33333 HR_REP 101 6500 PR_REP 101 10000 ST_CLERK 123 3000 SH_CLERK 121 3675 PU_CLERK 114 2780 SA_MAN 100 12200 MK_REP 201 6000 110 AC_ACCOUNT 8300 90 AD_VP 17000 50 ST_CLERK 2785 80 SA_REP 8396.55172 50 ST_MAN 7280 80 SA_MAN 12200 110 AC_MGR 12000 90 AD_PRES 24000 60 IT_PROG 5760 100 FI_MGR 12000 DEPARTMENT_ID JOB_ID MANAGER_ID AVG(SALARY) ------------- ---------- ---------- ----------- 30 PU_CLERK 2780 50 SH_CLERK 3215 20 MK_MAN 13000 100 FI_ACCOUNT 7920 SA_REP 7000 70 PR_REP 10000 30 PU_MAN 11000 10 AD_ASST 4400 20 MK_REP 6000 40 HR_REP 6500 52 rows selected.

q2（UNION ALL）：

SELECT   NULL department_id, job_id, manager_id, AVG (salary)
    FROM employees
GROUP BY (job_id, manager_id)
UNION ALL
SELECT   department_id, job_id, NULL manager_id, AVG (salary)
    FROM employees
GROUP BY (department_id, job_id);


DEPARTMENT_ID JOB_ID     MANAGER_ID AVG(SALARY)
------------- ---------- ---------- -----------
              SH_CLERK          122        3200
              AC_MGR            101       12000
              ST_MAN            100        7280
              ST_CLERK          121        2675
              SA_REP            148        8650
              SH_CLERK          120        2900
              SH_CLERK          124        2825
              MK_MAN            100       13000
              AD_PRES                     24000
              FI_MGR            101       12000
              SA_REP            146        8500
              SH_CLERK          123        3475
              AD_ASST           101        4400
              IT_PROG           102        9000
              IT_PROG           103        4950
              FI_ACCOUNT        108        7920
              PU_MAN            100       11000
              ST_CLERK          122        2700
              SA_REP            145        8500
              AC_ACCOUNT        205        8300
              AD_VP             100       17000

DEPARTMENT_ID JOB_ID     MANAGER_ID AVG(SALARY)
------------- ---------- ---------- -----------
              ST_CLERK          120        2625
              ST_CLERK          124        2925
              SA_REP            147  7766.66667
              SA_REP            149  8333.33333
              HR_REP            101        6500
              PR_REP            101       10000
              ST_CLERK          123        3000
              SH_CLERK          121        3675
              PU_CLERK          114        2780
              SA_MAN            100       12200
              MK_REP            201        6000
          110 AC_ACCOUNT                   8300
           90 AD_VP                       17000
           50 ST_CLERK                     2785
           80 SA_REP                 8396.55172
           50 ST_MAN                       7280
           80 SA_MAN                      12200
          110 AC_MGR                      12000
           90 AD_PRES                     24000
           60 IT_PROG                      5760
          100 FI_MGR                      12000

DEPARTMENT_ID JOB_ID     MANAGER_ID AVG(SALARY)
------------- ---------- ---------- -----------
           30 PU_CLERK                     2780
           50 SH_CLERK                     3215
           20 MK_MAN                      13000
          100 FI_ACCOUNT                   7920
              SA_REP                       7000
           70 PR_REP                      10000
           30 PU_MAN                      11000
           10 AD_ASST                      4400
           20 MK_REP                       6000
           40 HR_REP                       6500

52 rows selected.