Problem with minus

Question

Hi ,
I am facing a strange issue with the MINUS operator in Oracle.
Select count(1) from (query 1);
COUNT(1)
5298
Select count(1) from (query2);
COUNT(1)
5285
I am doing a minus to try to get the extra rows fetched by query 1 (both are selecting the same columns) :-
Query 1
MINUS
Query 2
However in this case is am getting :-
No rows selected
Please let me know any possible reasons for the same.
Thanks,
Suman

Answer 1

what is the distinct count in your first query. minus takes only the distinct values.
say your first query has 10 value of which the distinct count will be 5
and second query has 5 values (which is the same as the distinct values in query 1)
then query 1 - query 2 will give you no rows.
see this example...
SQL> select * from v$version;
BANNER
Oracle9i Enterprise Edition Release 9.2.0.1.0 - 64bit Production
PL/SQL Release 9.2.0.1.0 - Production
CORE 9.2.0.1.0 Production
TNS for Solaris: Version 9.2.0.1.0 - Production
NLSRTL Version 9.2.0.1.0 - Production
SQL> select *
2 from (select mod(level,5) from dual connect by level <= 10)
3 /
MOD(LEVEL,5)
1
2
3
4
0
1
2
3
4
0
10 rows selected.
SQL> select *
2 from (select mod(level,5) from dual connect by level <= 5)
3 /
MOD(LEVEL,5)
1
2
3
4
0
SQL> select *
2 from (select mod(level,5) from dual connect by level <= 10)
3 minus
4 select *
5 from (select mod(level,5) from dual connect by level <= 5)
6 /
no rows selected