On 05/24/2012 03:22 AM, Jacopo Cappellato wrote: > > On May 24, 2012, at 9:04 AM, Jacques Le Roux wrote: > >> From: "Jacopo Cappellato" <jacopo.cappell...@hotwaxmedia.com> >>> On May 23, 2012, at 9:25 PM, Adam Heath wrote: >>> >>>> On 05/23/2012 01:13 PM, Jacopo Cappellato wrote: >>>>> Using count() was simply a trick to be sure to get a record back even if >>>>> the entity is empty... but if we use an entity that we are sure is >>>>> populated we don't have to use it, of course. Of course if we use >>>>> count(*) we have to use it in an entity with a very low number of rows... >>>>> but I too would prefer to avoid it. >>>> >>>> select 1; >>> >>> Thank you Adam, this is the "trick" I was looking for when I mentioned >>> option #3 in my first email. >>> I will test the system with it and then commit. >>> >>> Jacopo >> >> Which entity will you use Jacopo? > > When I first saw Adam's comment I thought he was suggesting to simply execute > > "select 1" > > in order to run a "query" with no table to return a "record" with one field > containing 1. > But I maybe misunderstood the suggestion and at least on Derby this doesn't > seem to work; but I still need to fully test. > In my opinion adding a new entity for this would be an overkill; one solution > could be the following: > > select count(key_name) from entity_key_store where 1 = 2
Ah, grr, I'm so used to postgres, sorry for the trick not working. In oracle, postgres, and mysql, the following works. It returns 0 rows, but tests the connection, and sql parsing in the server. Would this be good enough? select 1 from entity_key_store where key_name = '' limit 1; Using '1 = 2' still causes a SEQ_SCAN on the table(explain in postgres says this). key_name has an index on it, so that part is faster. Since key_name is the primary key, you might not need the limit, but it couldn't hurt(except for a slightly slower parsing of the sql).
