Select MOD(rownum,2) gf from a WHERE gf=0

Question

hi all
select MOD(rownum,2) gf from a
where gf=0;
this query dod't give me rows
SQL> select MOD(rownum,2) gf from a;
        GF
         1
         0
         1
         0
         1
         0
6 rows selected.Please correct me
Thanks And Regards
Vikas
Edited by: vikas singhal on May 28, 2011 5:02 PM
Edited by: vikas singhal on May 28, 2011 5:03 PM

Answer 1

Hi, Vikas,
When you define a column alias (such as gf), you can use that alias in the ORDER BY clause, but that's the only place where you can use it in the same query. If you assign the alias in a sub-query, then you can use it anywhere in a super-query, like this:
WITH     got_gf     AS
     select      MOD (rownum, 2)      AS gf
     from      a
SELECT     *
FROM     got_gf
where      gf     = 0;If the aliased expression is simple, and you don't need to reference it often, then you may find it easier just to repeat the expression, like this:
select      MOD (rownum, 2)      AS gf
from      a
where      MOD (rownum, 2)     = 0;Edited by: Frank Kulash on May 28, 2011 8:04 AM
Correction: repeating the expression in the WHERE clause doesn't always work when it involves ROWNUM, since ROWNUM depends on how many previous rows satisfied the WHERE clause. In this case, use a sub-query.