Select query with column names takes longer

Hi Gurus,

If I am doing a select like:

Select * from table1 where a in (select b from table2 where c||d='x1234');

It takes .22 ms time, which is great. Both c and d columns have indices.

But if I run:

Select m, n from table1 where a in (select b from table2 where c||d='x1234');

It takes nore than 1 min if I only want columns m & n of the same table. Can you please help me understand why so?

Thanks

Samrat