SQL语句——15、高级分组

rollup 和 cube 

group by 生成数据结果时,只会生成相关列的数据统计信息,而不是生成小计和总计

group by统计结果如下(不是select直接返回格式):

SQL> select deptno,job,avg(sal) from emp group by deptno,job;
--------------------------------------------------------------
|deptno\job| clerk | analyst | manager | president | salesman |--------------------------------------------------------------
| 10      | 1300 |          | 2450    | 5000      |         |
--------------------------------------------------------------
| 20      | 950  |   3000   | 2975    |           |         |
--------------------------------------------------------------
| 30      | 950  |          | 2850    |           | 1400    |
--------------------------------------------------------------

rollup操作在保留group by统计结果的基础上,还会生成横向小计(部门平均工资)和总计(所有员工的平均工资)

select deptno,job,avg(sal) from emp group by rollup(deptno,job);
-----------------------------------------------------------------------------
|deptno\job | clerk | analyst | manager | president | salesman | 小计        |-----------------------------------------------------------------------------
| 10        | 1300  |         | 2450    | 5000      |          | 2916.66667 |
-----------------------------------------------------------------------------
| 20        | 950   | 3000    | 2975    |           |          | 2175       |
-----------------------------------------------------------------------------
| 30        | 950   |         | 2850    |           | 1400     | 1566.66667 |
-----------------------------------------------------------------------------
| 合计       |       |         |         |           |          | 2073.21429 |
-----------------------------------------------------------------------------

cube 是在group by rollup 的基础上,再做出纵向小计:

SQL> select deptno,job,avg(sal) from emp group by cube(deptno,job);
-----------------------------------------------------------------------------
|deptno\job | clark | analyst | manager | president | salesman | 小计        |-----------------------------------------------------------------------------
| 10        | 1300  || 2450    | 5000      |          | 2916.66667 |
-----------------------------------------------------------------------------
| 20        | 950   | 3000    | 2975    |           |          | 2175       |
-----------------------------------------------------------------------------
| 30        | 950   |         | 2850    |           | 1400     | 1566.66667 |
-----------------------------------------------------------------------------
| 职位小计   |1037.5 | 3000     |2758.333 | 5000     | 1400      |            |
-----------------------------------------------------------------------------
| 合计      |       |          |         |           |          | 2073.21429 |
-----------------------------------------------------------------------------

ROLLUP sql写法:

SQL> select deptno,job,avg(sal) from emp group by rollup (deptno,job);

DEPTNO        JOB     AVG(SAL)
---------- --------- ----------
10          CLERK      1300
10          MANAGER    2450
10          PRESIDENT  5000
10                     2916.66667
20          CLERK      950
20          ANALYST    3000
20          MANAGER    2975
20                     2175
30          CLERK      950
30          MANAGER    2850
30          SALESMAN   1400
30                     1566.66667
                       2073.21429

13 rows selected.

CUBE sql写法:

SQL> select deptno,job,avg(sal) from emp group by cube (deptno,job) order by 1;

DEPTNO         JOB     AVG(SAL)
---------- --------- ----------
10           CLERK      1300
10           MANAGER    2450
10           PRESIDENT  5000
10                      2916.66667
20           ANALYST    3000
20           CLERK      950
20           MANAGER    2975
20                      2175
30           CLERK      950
30           MANAGER    2850
30           SALESMAN   1400
30                      1566.66667
             ANALYST    3000
             CLERK      1037.5
             MANAGER    2758.33333
             PRESIDENT  5000
             SALESMAN   1400
                        2073.21429

18 rows selected.

解析rollup语句

rollup(a,b,c)

等同于

group by a,b,c
union all
group by a,b
union all
group by a
union all
group by null

为维持输出列的数量一直 select子句中用null来代替

举例:

SQL> select deptno,job,sum(sal) from emp group by rollup(deptno,job);

DEPTNO        JOB     SUM(SAL)
---------- --------- ----------
          CLERK     1300
          MANAGER   2450
          PRESIDENT 5000
                    8750
          CLERK     1900
          ANALYST   6000
          MANAGER   2975
                    10875
          CLERK     950
          MANAGER   2850
          SALESMAN  5600
                    9400

rows selected.

-----分解为:
SQL> select deptno,job,sum(sal) from emp group by deptno,job
union all
select deptno,null,sum(sal) from emp group by deptno
union all
select null,null,sum(sal) from emp
order by 1;

DEPTNO        JOB     SUM(SAL)
---------- --------- ----------
           CLERK     1300
                     8750
           MANAGER   2450
           PRESIDENT 5000
           ANALYST   6000
           MANAGER   2975
           CLERK     1900 
                     10875
           SALESMAN  5600
           CLERK     950
           MANAGER   2850
                     9400

rows selected.

解析cube语句

cube(a,b,c) 分解成2的N次方个union all组合

等同于:

group by a,b,c
union all
group by a,b
union all
group by a
union all
group by a,c
union all
group by b,c
union all
group by b
union all
group by c
union all
group by null

举例:

SQL> select deptno,job,sum(sal) from emp group by cube(deptno,job);

--------解析为:
SQL> select deptno,job,sum(sal) from emp group by deptno,job
union all
select deptno,null,sum(sal) from emp group by deptno
union all
select null,job,sum(sal) from emp group by job
union all
select null,null,sum(sal) from emp
order by 1

grouping

在使用rollup和cube时统计结果可能用到一列也可能用到多列,为了确定统计结果是否使用了特定列才使用grouping

返回为0 代表使用了该列

返回为1 代表没使用该列

SQL> select deptno,job,avg(sal),grouping(deptno),grouping(job) from emp
group by cube (deptno,job) order by 1;

DEPTNO        JOB       AVG(SAL) GROUPING(DEPTNO) GROUPING(JOB)
---------- --------- ---------- ---------------- -------------
10           CLERK       1300         0                0
10           MANAGER     2450         0                0
10           PRESIDENT   5000         0                0
10                       2916.66667   0                1
20           ANALYST     3000         0                0
20           CLERK       950          0                0
20           MANAGER     2975         0                0
20                       2175         0                1
30           CLERK       950          0                0
30           MANAGER     2850         0                0
30           SALESMAN    1400         0                0
30                       1566.66667   0                1
             ANALYST     3000         1                0
             CLERK       1037.5       1                0
             MANAGER     2758.33333   1                0
             PRESIDENT   5000         1                0
             SALESMAN    1400         1                0
                         2073.21429   1                1

18 rows selected.

grouping sets

GROUPING SETS是一个GROUP BY的增强语句,能让你随心所欲的指定多个分组列小计或合计,ORACLE会用UNION ALL将GROUPING SETS中制定的每组合计组合在一起。

GROUPING SETS相对与多个GROUP BY的优势:

  1. 只要一次扫描基表,能得到更好的性能
  2. 不需要写复杂的UNION语句
select deptno,job,avg(sal) from emp group by grouping sets(deptno,job);
--------实际就是两个group by的union all--------
select deptno,null,avg(sal) from emp group by deptno
union all
select null,job,avg(sal) from emp group by job;

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