Build numbers table on the fly in Oracle

Question

How do I return a rowset consisting of the last four years based on the current date?

If this query runs on 12/31/2010 it should return:

2007
2008
2009
2010

But if it is run on 1/1/2011 it should return:

2008
2009
2010
2011

Here's what I started with, two queries that return the starting year. I prefer the second as converting to string feels a bit dirty to me.

SELECT TO_CHAR(TRUNC(sysdate, 'YY') - INTERVAL '3' YEAR, 'YYYY') FROM DUAL;
SELECT EXTRACT (YEAR FROM sysdate) - 3 FROM DUAL;

But I don't know how to generate rows to flesh this out. In SQL Server I'd use a CTE as in the fn_nums function on this page.

Answer 1

Here is one way:

  SELECT yr
    FROM (    SELECT EXTRACT (YEAR FROM (ADD_MONTHS ( SYSDATE, - ( (LEVEL - 1) * 12)))) yr
                FROM DUAL
          CONNECT BY LEVEL <= 4)
ORDER BY yr;

Or:

  SELECT yr
    FROM (    SELECT  EXTRACT (YEAR FROM sysdate) - (level -1 ) yr
                FROM DUAL
          CONNECT BY LEVEL <= 4)
ORDER BY yr;

Or:

    SELECT yr
      FROM (SELECT EXTRACT (YEAR FROM SYSDATE) - (x - 1) yr
              FROM DUAL
            MODEL
               DIMENSION BY (1 AS z)
               MEASURES (1 x)
               RULES
                  ITERATE (4)
                  (x [ITERATION_NUMBER] = ITERATION_NUMBER + 1))
  ORDER BY yr;

Answer 2

To display numbers from 1 to 100:

SELECT  LEVEL 
FROM DUAL
CONNECT BY LEVEL <= 100
ORDER BY LEVEL

To change the max, change it in the third line.

Answer 3

Similar to the accepted answer you can replace the inline view with a with clause. I find the with clause more readable. In particular if you are going to perform multiple calculations against the on-the-fly NUMBERS table as part of the same query - the entire SQL statement is more readable.

Numbers table on the fly:

WITH NUMBERS_START_AT_ZERO AS
     (SELECT LEVEL - 1 AS NUM 
       FROM DUAL
       CONNECT BY LEVEL <= 4
       order by NUM desc)
SELECT  EXTRACT (YEAR FROM sysdate) - NUM AS YEARS
  FROM NUMBERS_START_AT_ZERO

Output:

YEARS
2009
2010
2011
2012