Performance issue with select statement

Hi Experts,

I have a select statement with inner join and for all entries.

Eg : it_data has 50,000 records.

while sy-subrc eq 0.

select a~field1 a~field2 a~field3 a~field4

          b~field1 b~field2 b~field3 into table it_temp

         from Zxxxxx as a inner join Zyyyyyy as b

        on a~field1 eq b~field1

for all entries in it_data where a~field1 in s_field1

and a~field2 in s_field2 and b~field3 = it_data-field5.

endwhile.

Note: Zxxxxx has 10000 records and Zyyyyyy has 4000 records.

Problem : taking long time for execution. its a performance issue.

3doubts: 1) Can I use for all entries with inner joins with huge data.

             2) I want to replace for all entries with Ranges..............with huge data...............is it work.

             3) What about While.....endwhile loop............?

Please Suggest me.

Thanks in advance.