Le 28/03/2015 19:09, Benoît Minisini a écrit : > Le 28/03/2015 18:58, Lewis Balentine a écrit : >> I have over three decades of dealing with SQL and I can still not >> understand how this myth got propagated. >> >> There is NO valid SQL reason why a table should be required to have a >> unique primary key or any predefined key for that matter. One can always >> use the row number (record number) if such a key is required for one's >> application. >> > > The row number does not exist in all database systems (more precisely, > it is not accessible to the outside), so I can't rely on that feature to > identify a row uniquely. > > Maybe the row id is not standard SQL, if "standard SQL" has any meaning. > > Consequently, I need a unique index, usually the primary key. > > If you can tell me how to get the row id of a row in MySQL, PostgreSQL > and SQLite (mabe it has changed since the last time I looked at it), I > will reconsider my position. :-) > > Regards, >
More explanations... I said "row number", I wanted to say "row id". MySQL has no row id concept apparently. PostgreSQL has something like that, but apparently not useful. SQLite has. The answer is always the same: you need a "row id"? Add a unique primary key based on a serial/auto-increment integer field. Now as for as "row number". I could use the "LIMIT / OFFSET" syntax to return the different part of a request, instead of using "LIMIT" + a criteria on the primary key. Alas PostgreSQL (for example), tells us that two identical "LIMIT / OFFSET" on the same request does not necessarily return the same records, unless you specify an predictible "ORDER BY" clause. Moreover "OFFSET" is not optimized on PostgreSQL. So I don't see a better solution than the current one. -- Benoît Minisini ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Gambas-user mailing list Gambas-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gambas-user
