DDS help please

We have a simple query on a file containing invoice information. The
invoice number is the key value and is a numeric 6 field with no
decimals.

I now need to add one piece of info from another file.  My problem is
that in the other file the invoice number is stored left justified in a
22 character field.

I studied the DDS manual that says I can convert character to numeric if
the characters are all digits but I can't come up with the logical file
that will compile.

I can use SST(char_22_field 1 6) and get a 6 character invoice number
but that does me no good with the joining of the 2 files in query.

Can I create a logical file with a 6 digit invoice number from the 22
character field in the physical file?

Thanks,
Greg