I believe that is a bit too complicated to do with SQL. However, I have the following suggestions for improving your code:

1) Don't abbreviate commands. It makes code more difficult to read.

2) Instead of SCATTER MEMVAR, it is probably better to use SCATTER NAME ... This will generate a single variable, similar to an object, and you can then access its properties by name.

3) To loop through all the records of a table, use SCAN ... ENDSCAN. This way, you don't need (a) the GO TOP, (b) the condition (WHILE NOT EOF(...)), and (c) the SKIP at the end of the loop.

>

>use 1001\customer again in 0 alias oldcustomer shared 
>use 1002\customer again in 0 alias newcustomer shared
>sele newcustomer
>set order to accode
>sele oldcustomer
>set order to accode
>go top
>do while not eof('oldcustomer')
>     scatter memvar
>     sele newcustomer
>     if  not seek(m.accode,'newcustomer','accode')
>         appe blank in newcustomer
>         gather memvar
>    else
>          if empt(newcustomer.address1)
>             repl newcustomer.address1 with m.address1 in newcustomer
>         endif
>          if empt(newcustomer.address2)
>             repl newcustomer.address2 with m.address2 in newcustomer
>         endif
>    endif
>    sele oldcustomer
>    skip
>enddo
>
>

>
>how to do this with sql.
>
>Warm regards,
>mk.