On 31 January 2016 at 19:53, David G. Johnston <david.g.johnston@xxxxxxxxx> wrote: > A PRIMARY KEY enforces a UNIQUE, NOT NULL constraint and additionally allows [snip] I would just remove the whole paragraph. A primary key does what it does, a unique constraint does what it does. I'm not really sure why you need to link them. I would just start with "A primary key indicates that a column or group of columns can be used as a unique identifier for rows in the table." before the examples, then remove the "Technically" and the whole parenthesised comment about unique keys and nulls, so the next line after the examples becomes "Primary keys are useful both for documentation purposes and for client applications. For example, a GUI application that allows modifying row values probably needs to know the primary key of a table to be able to identify rows uniquely." I just think it's unnecessarily confusing to start suggesting that there's some equivalency when you then need to clarify that actually they're not really equivalent. Geoff -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
