Thank you Naomi and Sergey. That clears it up for me.

>Elgin,
>
>The first way is preferrable especially if you plan to port to SQL Server. The first way will be better if you have individual indexes on each field.
>If you have a compound index with CustID + UpsiNo as its expression, then the second variation will be better from Rushmore optimization point of the view.
>
>
>>Basic question(s):
>>
>>Two examples: the two fields I'm joining on are of the same data type:
>>
>>Example 1:
>>SELECT v.*
>>FROM visual v
>>INNER JOIN nameplate n
>>ON v.custid = n.custid AND v.upsino = n.upsino
>>WHERE v.custid = lcCustid
>>ORDER BY v.custid, v.upsino
>>
>>Example2:
>>SELECT v.*
>>FROM visual v
>>INNER JOIN nameplate n
>>ON (v.custid + v.upsino) = (n.custid + n.upsino)
>>WHERE v.custid = lcCustid
>>ORDER BY v.cusid, v.upsino
>>
>>Are both join conditions acceptable? Which is more efficient?
>>
>>Will I get into trouble using either one? Is there a standard?
>>
>>What if the join condition involves more that two fields of the same data type? Is it still OK to concatenate?
>>
>>Thank You for your help.