>> I presume this is considered a mistake only because of SQL allowing duplicate "rows". In the real RM, no such mistake is possible. <<
No, we would have Dr. Codd's "Degree of Duplication" operator that
nobody mentions. This is how he handled dups in RM II. At least you
can avoid dups in base tables in SQL via constraints and in results via
SELECT DISTINCT.
Teradata used to disallow duplicate rows in its early versions, but
lost out to Standard SQL. My wish is that we had put in a [CREATE |
DECLARE] FILE <name> (<column list>) construct for the non-tables. But
SQL was built on the existing indexed file systems of the day, and we
are stuck with the family legacy (aka "family curse").
Received on Sat Jun 10 2006 - 18:19:44 CDT
