same select statement taking more time

Hello all,

I have two select statements. only the name of table from where it is fetching records are different.

1) select belnr posnr etenr into corresponding fields of table it_cdtemp2

from j_3avasso for all entries in it_cdtemp1

where belnr = it_cdtemp1-vbeln and posnr = it_cdtemp1-posnr .

it_cdtemp1 has 100 entries and j_3avasso has 20000 entries

2) select belnr posnr etenr into corresponding fields of table it_cdtemp2

from j_3avap for all entries in it_cdtemp1

where belnr = it_cdtemp1-vbeln and posnr = it_cdtemp1-posnr .

it_cdtemp1 has 100 entries and j_3avasso has 2000 entries

statement 1 is executing less than a minute where as statement 2 is taking around 15 to 20 minutes

could anyone suggest why.. if so how to minimize run time

Regards

Bala