DECODE in the GROUP BY clause : DECODE « Conversion Functions « Oracle PL/SQL Tutorial

SQL>
SQL> create table emp(
  2           emp_no                 integer         primary key
  3          ,lastname               varchar2(20)    not null
  4          ,firstname              varchar2(15)    not null
  5          ,midinit                varchar2(1)
  6          ,street                 varchar2(30)
  7          ,city                   varchar2(20)
  8          ,state                  varchar2(2)
  9          ,zip                    varchar2(5)
 10          ,shortZipCode           varchar2(4)
 11          ,area_code              varchar2(3)
 12          ,phone                  varchar2(8)
 13          ,salary                 number(5,2)
 14          ,birthdate              date
 15          ,startDate              date
 16          ,title                  varchar2(20)
 17          ,dept_no                integer
 18          ,mgr                    integer
 19          ,region                 number
 20          ,division               number
 21          ,total_sales            number
 22  );

Table created.

SQL>
SQL> -- emp Table Inserts:
SQL> insert into emp(emp_no, lastname, firstname, midinit, street, city, state, zip,shortZipCode, area_code, phone, birthdate, title)values
  2                      (1,'Z','Joy','R','1 Ave','New York','NY','12122','2333','212','200-1111','12-nov-1976','President');

1 row created.

SQL>
SQL>
SQL> create or replace view avg_Sal
  2  as select trunc(avg(salary)) avg_sal
  3  from emp
  4  /

View created.

SQL>
SQL>
SQL> select
  2  decode(  sign( (salary - avg_sal ) ),
  3       1, '> Average of ' || to_char(avg_sal, '99.99') ,
  4       0, '= Average of ' || to_char(avg_sal, '99.99'),
  5          -1, '< Average of ' || to_char(avg_sal, '99.99')  ) sal_desc,
  6   count(*)
  7  from emp, avg_sal
  8  group by
  9  decode(  sign( (salary - avg_sal ) ),
 10       1, '> Average of ' || to_char(avg_sal, '99.99') ,
 11       0, '= Average of ' || to_char(avg_sal, '99.99'),
 12          -1, '< Average of ' || to_char(avg_sal, '99.99')  )
 13  /

                             1

1 row selected.

SQL>
SQL> drop table emp;

Table dropped.

15.2.DECODE
	15.2.1.	Using the DECODE() Function
	15.2.2.	SELECT DECODE(1, 2, 1, 3)
	15.2.3.	Use Decode in table column
	15.2.4.	Pass multiple search and result parameters to DECODE()
	15.2.5.	The null may be made more explicit with a DECODE statement
	15.2.6.	Decode as If statement
	15.2.7.	Demo range comparison with DECODE
	15.2.8.	DECODE in the GROUP BY clause
	15.2.9.	Use decode create dynamic select statement
	15.2.10.	Use decode as if statement and output 'high' or 'low'
	15.2.11.	decode column data to output more meaningful information