Use decode create dynamic select statement : DECODE « Conversion Functions « Oracle PL/SQL Tutorial

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2. Conversion Functions
3. DECODE

SQL> CREATE TABLE EMP(
  2      EMPNO NUMBER(4) NOT NULL,
  3      ENAME VARCHAR2(10),
  4      JOB VARCHAR2(9),
  5      MGR NUMBER(4),
  6      HIREDATE DATE,
  7      SAL NUMBER(7, 2),
  8      COMM NUMBER(7, 2),
  9      DEPTNO NUMBER(2)
 10  );

Table created.

SQL>
SQL> INSERT INTO EMP VALUES(7369, 'SMITH', 'CLERK', 7902,TO_DATE('17-DEC-1980', 'DD-MON-YYYY'), 800, NULL, 20);

1 row created.

SQL> INSERT INTO EMP VALUES(7499, 'ALLEN', 'SALESMAN', 7698,TO_DATE('20-FEB-1981', 'DD-MON-YYYY'), 1600, 300, 30);

1 row created.

SQL> INSERT INTO EMP VALUES(7521, 'WARD', 'SALESMAN', 7698,TO_DATE('22-FEB-1981', 'DD-MON-YYYY'), 1250, 500, 30);

1 row created.

SQL> INSERT INTO EMP VALUES(7566, 'JONES', 'MANAGER', 7839,TO_DATE('2-APR-1981', 'DD-MON-YYYY'), 2975, NULL, 20);

1 row created.

SQL> INSERT INTO EMP VALUES(7654, 'MARTIN', 'SALESMAN', 7698,TO_DATE('28-SEP-1981', 'DD-MON-YYYY'), 1250, 1400, 30);

1 row created.

SQL> INSERT INTO EMP VALUES(7698, 'BLAKE', 'MANAGER', 7839,TO_DATE('1-MAY-1981', 'DD-MON-YYYY'), 2850, NULL, 30);

1 row created.

SQL> INSERT INTO EMP VALUES(7782, 'CLARK', 'MANAGER', 7839,TO_DATE('9-JUN-1981', 'DD-MON-YYYY'), 2450, NULL, 10);

1 row created.

SQL> INSERT INTO EMP VALUES(7788, 'SCOTT', 'ANALYST', 7566,TO_DATE('09-DEC-1982', 'DD-MON-YYYY'), 3000, NULL, 20);

1 row created.

SQL> INSERT INTO EMP VALUES(7839, 'KING', 'PRESIDENT', NULL,TO_DATE('17-NOV-1981', 'DD-MON-YYYY'), 5000, NULL, 10);

1 row created.

SQL> INSERT INTO EMP VALUES(7844, 'TURNER', 'SALESMAN', 7698,TO_DATE('8-SEP-1981', 'DD-MON-YYYY'), 1500, 0, 30);

1 row created.

SQL> INSERT INTO EMP VALUES(7876, 'ADAMS', 'CLERK', 7788,TO_DATE('12-JAN-1983', 'DD-MON-YYYY'), 1100, NULL, 20);

1 row created.

SQL> INSERT INTO EMP VALUES(7900, 'JAMES', 'CLERK', 7698,TO_DATE('3-DEC-1981', 'DD-MON-YYYY'), 950, NULL, 30);

1 row created.

SQL> INSERT INTO EMP VALUES(7902, 'FORD', 'ANALYST', 7566,TO_DATE('3-DEC-1981', 'DD-MON-YYYY'), 3000, NULL, 20);

1 row created.

SQL> INSERT INTO EMP VALUES(7934, 'MILLER', 'CLERK', 7782,TO_DATE('23-JAN-1982', 'DD-MON-YYYY'), 1300, NULL, 10);

1 row created.

SQL>
SQL> create or replace function get_value_static( p_empno in number, p_cname in varchar2 ) return varchar2
  2  as
  3      l_value  varchar2(4000);
  4  begin
  5      select decode( upper(p_cname),
  6                    'ENAME', ename,
  7                    'EMPNO', empno,
  8                    'HIREDATE', to_char(hiredate,'yyyymmddhh24miss'))
  9        into l_value
 10        from emp
 11       where empno = p_empno;
 12
 13      return l_value;
 14  end;
 15  /

Function created.

SQL>
SQL>
SQL>
SQL> drop table emp;

Table dropped.