replace field1 with mytable1.field1, field2 with mytable1.field2, field3 with mytable1.field3 in mytable2

>hi all,
>
>how i can replace field1,2,3 from mytable1(mytable1 have 3 fields only), to mytable2 field1,2,3 but keep field4 as it is,
>
>somthing as scatter memvar from table1 ,gather memvar to table2.
>
>thanks.
>m.qasem