GROUPING函数可以接受一列，返回0或者1。如果列值为空，那么GROUPING()返回1；如果列值非空，那么返回0。GROUPING只能在使用ROLLUP或CUBE的查询中使用。当需要在返回空值的地方显示某个值时，GROUPING()就非常有用。
1、在ROLLUP中对单列使用GROUPING()
SQL> select division_id,sum(salary) 2 from employees2 3 group by rollup(division_id) 4 order by division_id; DIV SUM(SALARY) --- ----------- BUS 1610000 OPE 1320000 SAL 4936000 SUP 1015000 8881000
加上GROUPING来看看
SQL> select grouping(division_id),division_id,sum(salary) 2 from employees2 3 group by rollup(division_id) 4 order by division_id; GROUPING(DIVISION_ID) DIV SUM(SALARY) --------------------- --- ----------- 0 BUS 1610000 0 OPE 1320000 0 SAL 4936000 0 SUP 1015000 1 8881000
可以看到，为空的地方返回1，非空的地方返回0。
2、使用CASE转换GROUPING()的返回值
可能你会觉得前面的0和1太枯燥了，代表不了任何意义，说白了就是不够人性化，呵呵。这个时候我们可以使用CASE来转换为一些有意义的值。
SQL> select 2 case grouping(division_id) 3 when 1 then 'all divisions' 4 else division_id 5 end as div, 6 sum(salary) 7 from employees2 8 group by rollup(division_id) 9 order by division_id; DIV SUM(SALARY) ------------- ----------- BUS 1610000 OPE 1320000 SAL 4936000 SUP 1015000 all divisions 8881000
3、使用CASE和GROUPING()转换多个列的值
SQL> select 2 case grouping(division_id) 3 when 1 then 'all divisions' 4 else division_id 5 end as div, 6 case grouping(job_id) 7 when 1 then 'all jobs' 8 else job_id 9 end as job, 10 sum(salary) 11 from employees2 12 group by rollup(division_id,job_id) 13 order by division_id,job_id; DIV JOB SUM(SALARY) ------------- -------- ----------- BUS MGR 530000 BUS PRE 800000 BUS WOR 280000 BUS all jobs 1610000 OPE ENG 245000 OPE MGR 805000 OPE WOR 270000 OPE all jobs 1320000 SAL MGR 4446000 SAL WOR 490000 SAL all jobs 4936000 DIV JOB SUM(SALARY) ------------- -------- ----------- SUP MGR 465000 SUP TEC 115000 SUP WOR 435000 SUP all jobs 1015000 all divisions all jobs 8881000 16 rows selected.
4、CUBE与GROUPING()结合使用
SQL> select 2 case grouping(division_id) 3 when 1 then 'all divisions' 4 else division_id 5 end as div, 6 case grouping(job_id) 7 when 1 then 'all jobs' 8 else job_id 9 end as job, 10 sum(salary) 11 from employees2 12 group by cube(division_id,job_id) 13 order by division_id,job_id; DIV JOB SUM(SALARY) ------------- -------- ----------- BUS MGR 530000 BUS PRE 800000 BUS WOR 280000 BUS all jobs 1610000 OPE ENG 245000 OPE MGR 805000 OPE WOR 270000 OPE all jobs 1320000 SAL MGR 4446000 SAL WOR 490000 SAL all jobs 4936000 DIV JOB SUM(SALARY) ------------- -------- ----------- SUP MGR 465000 SUP TEC 115000 SUP WOR 435000 SUP all jobs 1015000 all divisions ENG 245000 all divisions MGR 6246000 all divisions PRE 800000 all divisions TEC 115000 all divisions WOR 1475000 all divisions all jobs 8881000 21 rows selected.
5、使用GROUPING SETS子句
使用GROUPING SETS子句可以只返回小计记录。
SQL> select division_id,job_id,sum(salary) 2 from employees2 3 group by grouping sets(division_id,job_id) 4 order by division_id,job_id; DIV JOB SUM(SALARY) --- --- ----------- BUS 1610000 OPE 1320000 SAL 4936000 SUP 1015000 ENG 245000 MGR 6246000 PRE 800000 TEC 115000 WOR 1475000 9 rows selected.
