Saturday, October 18, 2014

Oracle Group Functions with examples



GROUP BY AND HAVING


GROUP BY

Using group by, we can create groups of related information.
Columns used in select must be used with group by, otherwise it was not a group by expression.

Ex:
     SQL> select deptno, sum(sal) from emp group by deptno;

                        DEPTNO   SUM(SAL)
---------- ----------
        10       8750
        20      10875
        30       9400

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

                        DEPTNO  JOB         SUM(SAL)
---------- ---------   ----------
        10   CLERK            1300
        10   MANAGER      2450
        10   PRESIDENT   5000
        20   ANALYST       6000
        20   CLERK           1900
        20   MANAGER     2975
        30   CLERK             950
        30   MANAGER      2850
        30   SALESMAN    5600

HAVING

This will work as where clause which can  be used only with group by because of absence of where clause in group by.
Ex:
     SQL> select deptno,job,sum(sal) tsal from emp group by deptno,job having sum(sal) > 3000;

              DEPTNO   JOB              TSAL
   ----------  ---------      ----------
        10    PRESIDENT    5000
        20    ANALYST        6000
        30    SALESMAN     5600

SQL> select deptno,job,sum(sal) tsal from emp group by deptno,job having sum(sal) > 3000 
         order by job;

                   DEPTNO    JOB          TSAL
 ----------  ---------    ----------
          20          ANALYST       6000
                       10        PRESIDENT   5000
     30        SALESMAN    5600

ORDER OF EXECUTION

Ø  Group the rows together based on group by clause.
Ø  Calculate the group functions for each group.
Ø  Choose and eliminate the groups based on the having clause.
Ø  Order the groups based on the specified column.














ROLLUP GROUPING CUBE


These are the enhancements to the group by feature.

USING ROLLUP

This will give the salaries in each department in each job category along wih the total salary   
fot individual departments and the total salary of all the departments.

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

                        DEPTNO   JOB         SUM(SAL)
----------  ---------   ----------
        10    CLERK           1300
        10    MANAGER     2450
        10    PRESIDENT   5000
        10                          8750
        20    ANALYST       6000
        20    CLERK           1900
        20    MANAGER     2975
        20                        10875
        30    CLERK             950
        30    MANAGER      2850
        30    SALESMAN     5600
        30                          9400
                          29025

USING GROUPING

 In the above query it will give the total salary of the individual departments but with a  
 blank in the job column and gives the total salary of all the departments with blanks in
 deptno and job columns.
 
 To replace these blanks with your desired string grouping will be used
  SQL> select decode(grouping(deptno),1,'All Depts',deptno),decode(grouping(job),1,'All             
          jobs',job),sum(sal) from emp group by rollup(deptno,job);

DECODE(GROUPING(DEPTNO),1,'ALLDEPTS',DEP DECODE(GR   SUM(SAL)
-----------------------------------  ----------------------------------    --------------
10                                                        CLERK             1300
10                                                         MANAGER                 2450
10                                                        PRESIDENT               5000
10                                                        All jobs                       8750
20                                                        ANALYST                   6000
20                                                        CLERK             1900
20                                                        MANAGER                  2975
20                                                        All jobs                    10875
30                                                        CLERK              950
30                                                        MANAGER                  2850
30                                                        SALESMAN                 5600
30                                                        All jobs                       9400
All Depts                                                        All jobs                    29025

   Grouping will return 1 if the column which is specified in the grouping function has been
   used in rollup.
   Grouping will be used in association with decode.

USING CUBE

This will give the salaries in each department in each job category, the total salary for individual departments, the total salary of all the departments and the salaries in each job category.

SQL> select decode(grouping(deptno),1,’All Depts’,deptno),decode(grouping(job),1,’All 
        Jobs’,job),sum(sal) from emp group by cube(deptno,job);

DECODE(GROUPING(DEPTNO),1,'ALLDEPTS',DEP DECODE(GR   SUM(SAL)
-----------------------------------  ------------------------------------  ------------
10                                            CLERK                         1300
10                                            MANAGER                              2450
10                                            PRESIDENT                           5000
10                                            All Jobs                                  8750
20                                            ANALYST                               6000
20                                            CLERK                         1900
20                                            MANAGER                              2975
20                                            All Jobs                               10875
30                                            CLERK                            950
30                                            MANAGER                               2850
30                                            SALESMAN                             5600
30                                            All Jobs                                  9400
All Depts                                            ANALYST                               6000
All Depts                                            CLERK                         4150
All Depts                                            MANAGER                              8275
All Depts                                            PRESIDENT                           5000
All Depts                                            SALESMAN                             5600
All Depts                                            All Jobs                               29025




























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