Different number of rows when add/delete the same table

Question

Hi,
i've a problem in a select statement.
My database is a 9.2.0.8.
select *
from  tab1 t1,
        tab2 t2,
        tab2 t3
where t1.id_c1 = 1
   AND t1.id_c2 = t2.id_c2
   AND t1.id_c2 = t3.id_c2
   AND t2.id_init = 3693
   AND t3.id_init = 3892;
936 rows selected.if i change the query in:
select *
from  tab1 t1,
        tab2 t2
where t1.id_c1=1
   AND t1.id_c2 = t2.id_c2
   AND t2.id_init in ( 3693,3892);
61132 rows selected.Any ideas? what's wrong??
Tnx
Edited by: 842366 on 10-ago-2011 3.10
Edited by: 842366 on 10-ago-2011 3.10

Answer 1

You can see the difference yourself with this sample test data.
SQL> with t_data1 as
select 1 as id_c1,2 as id_c2 from dual union all
select 2 ,2 from dual
t_data2 as
select 1 as id_c2, 3693 as id_init from dual union all
select 1, 3693  from dual union all
select 1, 3892t from dual union all
select 1, 3892 from dual union all
select 2, 3693 from dual union all
select 2, 3892 from dual union all
select 2, 3892 from dual
select *
from  t_data1 t1,
        t_data2 t2
where t1.id_c1=1
   AND t1.id_c2 = t2.id_c2
   AND t2.id_init in ( 3693,3892);
     ID_C1      ID_C2      ID_C2    ID_INIT
         1          2          2       3693
         1          2          2       3892
         1          2          2       3892
SQL> SQL>
SQL>
SQL>
SQL> with t_data1 as
select 1 as id_c1,2 as id_c2 from dual union all
select 2 ,2 from dual
t_data2 as
select 1 as id_c2, 3693 as id_init from dual union all
select 1, 3693  from dual union all
select 1, 3892t from dual union all
select 1, 3892 from dual union all
select 2, 3693 from dual union all
select 2, 3892 from dual union all
select 2, 3892 from dual
select *
from  t_data1 t1,
        t_data2 t2,
        t_data2 t3
where t1.id_c1 = 1
   AND t1.id_c2 = t2.id_c2
   AND t1.id_c2 = t3.id_c2
   AND t2.id_init = 3693
   AND t3.id_init = 3892;
     ID_C1      ID_C2      ID_C2    ID_INIT      ID_C2    ID_INIT
         1          2          2       3693          2       3892
         1          2          2       3693          2       3892
SQL> We see that in both the queries, the no. of column returned are different. In first it is 4 and in 2nd it returns 6.
Now ask yourself, what is the use of this query, and how I am suppose to use the values returned and also what is the purpose for each value.
Once you have the answers for these questions, the requirement becomes more clearer, doubts vanish and more often you can do things yourself.