Max value of itab

Hi experts,

select * from cdhdr into table itab.

After this statement i have to select the max value of changenr record details from itab for each tcode.Please help me.

previously i used

select max( changenr ) from cdhdr into table

itab where...group by tcode.

loop at itab.

select * from cdhdr into table it_cdhdr.

endloop.

its working. but some performance issue is there.