Jim,

>If the combination of two fields comprises the primary key of a table, then those two fields should be in an index together so records can be found with a simple seek. Joins are based on the relationship of the primary key of one table and the foreign key in another table.

Well, here you have a point. For readability reason I might do the same thing

>The issue of data types is irrelavent. Data conversions are possible.

>WHERE STR(CustNo,10,0) + STR(InvNo,10,0) = ...

Yes, of course, But here you create a key which could not be as usable as two index keys (when it does not regard a PK or FK) because of rushmore optimization in other parts of the program. I simply try to avoid composite keys as much as posible.

>Using an AND in a JOIN condition is more complicated in my opinion as it conceals the PK and FK values

Well I think its just a matter of taste. Using the AND follows the ANSI SQL92 syntax while this solution might only apply to VFP.

Walter,