On Tue, Jun 28, 2005 at 10:21:16 -0400, Merlin Moncure <[EMAIL PROTECTED]> wrote: > I need a fast way (sql only preferred) to solve the following problem: > > I need the smallest integer that is greater than zero that is not in the > column of a table. In other words, if an 'id' column has values > 1,2,3,4,6 and 7, I need a query that returns the value of 5. > > I've already worked out a query using generate_series (not scalable) and > pl/pgsql. An SQL only solution would be preferred, am I missing > something obvious?
I would expect that using generate series from the 1 to the max (using order by and limit 1 to avoid extra sequential scans) and subtracting out the current list using except and then taking the minium value would be the best way to do this if the list is pretty dense and you don't want to change the structure. If it is sparse than you can do a special check for 1 and if that is present find the first row whose successor is not in the table. That shouldn't be too slow. If you are willing to change the structure you might keep one row for each number and use a flag to mark which ones are empty. If there are relatively few empty rows at any time, then you can create a partial index on the row number for only empty rows. ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly