Suppose I have a column to determine whether the employee is male or female. The values are M or F. How do I convert all M to F and all F to M?
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This one is really quite straightforward. You can simply use a CASE statement in the SET clause of your UPDATE statement to check to see what the GENDER value currently is and then set it to the opposing value. Here's an example using the familiar EMP table:
First, let's display the original data:
SQL> select * from emp;
EMPNO ENAME JOB G MGR HIREDATE SAL COMM DEPTNO
--------------- ---------- --------- - --------------- --------- --------------- --------------- ---------------
7369 SMITH CLERK M 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN M 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN M 7698 22-FEB-81 1250 500 30
7566 JONES MANAGER M 7839 02-APR-81 2975 20
7654 MARTIN SALESMAN F 7698 28-SEP-81 1250 1400 30
7698 BLAKE MANAGER M 7839 01-MAY-81 2850 30
7782 CLARK MANAGER M 7839 09-JUN-81 2450 10
7788 SCOTT ANALYST M 7566 19-APR-87 3000 20
7839 KING PRESIDENT M 17-NOV-81 5000
7844 TURNER SALESMAN M 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK F 7788 23-MAY-87 1100 20
7900 JAMES CLERK M 7698 03-DEC-81 950 30
7902 FORD ANALYST F 7566 03-DEC-81 3000 20
7934 MILLER CLERK M 7782 23-JAN-82 1300 10
14 rows selected.
Now, let's execute the update to flip-flop the GENDER values:
SQL> update emp 2 set gender = case when gender = 'F' then 'M' when gender = 'M' then 'F' end ; 14 rows updated.
Finally, let's verify the result:
SQL> select * from emp ;
EMPNO ENAME JOB G MGR HIREDATE SAL COMM DEPTNO
--------------- ---------- --------- - --------------- --------- --------------- --------------- ---------------
7369 SMITH CLERK F 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN F 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN F 7698 22-FEB-81 1250 500 30
7566 JONES MANAGER F 7839 02-APR-81 2975 20
7654 MARTIN SALESMAN M 7698 28-SEP-81 1250 1400 30
7698 BLAKE MANAGER F 7839 01-MAY-81 2850 30
7782 CLARK MANAGER F 7839 09-JUN-81 2450 10
7788 SCOTT ANALYST F 7566 19-APR-87 3000 20
7839 KING PRESIDENT F 17-NOV-81 5000
7844 TURNER SALESMAN F 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK M 7788 23-MAY-87 1100 20
7900 JAMES CLERK F 7698 03-DEC-81 950 30
7902 FORD ANALYST M 7566 03-DEC-81 3000 20
7934 MILLER CLERK F 7782 23-JAN-82 1300 10
14 rows selected.
This was first published in April 2010
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