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Oracle DBA FAQ - Understanding SQL Basics

By: FYIcenter.com

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(Continued from previous part...)

How To Convert Numbers to Characters?

You can convert numeric values to characters by using the TO_CHAR() function as shown in the following examples:

SELECT TO_CHAR(4123.4570) FROM DUAL
123.457

SELECT TO_CHAR(4123.457, '$9,999,999.99') FROM DUAL
     $4,123.46

SELECT TO_CHAR(-4123.457, '9999999.99EEEE') FROM DUAL
 -4.12E+03

How To Convert Characters to Numbers?

You can convert characters to numbers by using the TO_NUMBER() function as shown in the following examples:

SELECT TO_NUMBER('4123.4570') FROM DUAL
4123.457

SELECT TO_NUMBER('     $4,123.46','$9,999,999.99') FROM DUAL
4123.46

SELECT TO_NUMBER(' -4.12E+03') FROM DUAL
-4120

How To Convert Dates to Characters?

You can convert dates to characters using the TO_CHAR() function as shown in the following examples:

SELECT TO_CHAR(SYSDATE, 'DD-MON-YYYY') FROM DUAL;
  -- SYSDATE returns the current date
07-MAY-2006 

SELECT TO_CHAR(SYSDATE, 'YYYY/MM/DD') FROM DUAL;
2006/05/07 

SELECT TO_CHAR(SYSDATE, 'MONTH DD, YYYY') FROM DUAL;
MAY       07, 2006

SELECT TO_CHAR(SYSDATE, 'fmMONTH DD, YYYY') FROM DUAL;
May 7, 2006

SELECT TO_CHAR(SYSDATE, 'fmDAY, MONTH DD, YYYY') FROM DUAL;
SUNDAY, MAY 7, 2006 

How To Convert Characters to Dates?

You can convert dates to characters using the TO_DATE() function as shown in the following examples:

SELECT TO_DATE('07-MAY-2006', 'DD-MON-YYYY') FROM DUAL;
07-MAY-06

SELECT TO_DATE('2006/05/07 ', 'YYYY/MM/DD') FROM DUAL;
07-MAY-06

SELECT TO_DATE('MAY       07, 2006', 'MONTH DD, YYYY')
  FROM DUAL;
07-MAY-06

SELECT TO_DATE('May 7, 2006', 'fmMONTH DD, YYYY') FROM DUAL;
07-MAY-06

SELECT TO_DATE('SUNDAY, MAY 7, 2006', 
  'fmDAY, MONTH DD, YYYY') FROM DUAL;
07-MAY-06 

How To Convert Times to Characters?

You can convert dates to characters using the TO_CHAR() function as shown in the following examples:

SELECT TO_CHAR(SYSDATE, 'HH:MI:SS') FROM DUAL;
04:49:49

SELECT TO_CHAR(SYSDATE, 'HH24:MI:SS.FF') FROM DUAL;
  -- Error: SYSDATE has no fractional seconds
  
SELECT TO_CHAR(SYSTIMESTAMP, 'HH24:MI:SS.FF9') FROM DUAL;
16:52:57.847000000                     

SELECT TO_CHAR(SYSDATE, 'SSSSS') FROM DUAL;
  -- Seconds past midnight
69520

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