Oracle DBA FAQ - Understanding SQL Basics

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By: FYIcenter.com

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(Continued from previous part...)

How To Concatenate Two Text Values?

There are two ways to concatenate two text values together:

CONCAT() function.
'||' operation.

Here is some examples on how to use them:

SELECT 'FYI' || 'Center' || '.com' FROM DUAL;
FYICenter.com 

SELECT CONCAT('FYICenter','.com') FROM DUAL;
FYICenter.com

How To Increment Dates by 1?

If you have a date, and you want to increment it by 1. You can do this by adding the date with a date interval. You can also do this by adding the number 1 directly on the date. The tutorial example below shows you how to adding numbers to dates, and take date differences:

SELECT TO_DATE('30-APR-06') + 1 FROM DUAL;
  -- Adding 1 day to a date
01-MAY-06 

SELECT TO_DATE('01-MAY-06') - TO_DATE('30-APR-06')
  FROM DUAL;
  -- Taking date differences
1

SELECT SYSTIMESTAMP + 1 FROM DUAL;
  -- The number you add is always in days.
08-MAY-06

SELECT TO_CHAR(SYSTIMESTAMP+1,'DD-MON-YYYY HH24:MI:SS.FF3')
  FROM DUAL;
-- Error: Adding 1 to a timestamp makes it a date.

How To Calculate Date and Time Differences?

If you want to know how many years, months, days and seconds are there between two dates or times, you can use the date and time interval expressions: YEAR ... TO MONTH and DAY ... TO SECOND. The tutorial exercise below gives you some good examples:

SELECT
  (TO_DATE('01-MAY-2006 16:52:57','DD-MON-YYYY HH24:MI:SS')
   - 
   TO_DATE('31-JAN-1897 09:26:50','DD-MON-YYYY HH24:MI:SS'))
  YEAR(4) TO MONTH FROM DUAL;
  -- 109 years and 3 months
109-3  

SELECT 
  (TO_DATE('01-MAY-2006 16:52:57','DD-MON-YYYY HH24:MI:SS')
   - 
   TO_DATE('31-JAN-1897 09:26:50','DD-MON-YYYY HH24:MI:SS'))
  DAY(9) TO SECOND FROM DUAL;
  -- 39901 days and some seconds
39901 7:26:7.0  

SELECT 
  (TO_TIMESTAMP('01-MAY-2006 16:52:57.847',
  'DD-MON-YYYY HH24:MI:SS.FF3') - 
   TO_TIMESTAMP('31-JAN-1897 09:26:50.124',
  'DD-MON-YYYY HH24:MI:SS.FF3'))
  YEAR(4) TO MONTH FROM DUAL;
  -- 109 years and 3 months
109-3  

SELECT 
  (TO_TIMESTAMP('01-MAY-2006 16:52:57.847',
  'DD-MON-YYYY HH24:MI:SS.FF3') - 
   TO_TIMESTAMP('31-JAN-1897 09:26:50.124',
  'DD-MON-YYYY HH24:MI:SS.FF3'))
  DAY(9) TO SECOND
  FROM DUAL;
  -- 39901 days and some fractional seconds
39901 7:26:7.723000000 

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