I’m reading a <a href=”http://www.progress.com/progress/products/documentation/docs/database/dbd/dbd.pdf”>Progress documentation pdf</a> and it says:
“7.1.2 PRIMARY Constraint
Use this constraint to name one or more columns to uniquely identify a row in a table. There can
only be one primary key for a table. <b><i>These columns cannot contain null values</i></b>.”
However, if null values were allowed, I don’t think it could affect performance, because in any case, the combination of all primary key fields in compound keys should be unique. Is there a specific reason why you think that could happen ?