This
implies no duplicate rows. Relational systems work on sets of rows distinguished
by data value. It is impossible to distinguish duplicate rows, making it
difficult to manipulate the duplicates independently. dB2K handles duplicate
rows better than many systems. Still, try writing an SQL query that only
deletes one of two duplicate rows! Some other relational systems even throw
the extra row away as useless and meaningless. Save yourself trouble, design
your database so that you don't permit duplicate rows in your tables.