On Fri, Aug 14, 2009 at 12:04 AM, David Kerr<dmk@xxxxxxxxxxxxxx> wrote: > On Thu, Aug 13, 2009 at 05:28:01PM +0100, Richard Huxton wrote: > - David Kerr wrote: > - > > - >create view test as > - >select a,b,c,d,e,f,g from testtable; > - > > - >select a from test; > - > > - >(does the engine retrieve b-g?) > - > - Shouldn't - the query just gets rewritten macro-style. I don't think it > - eliminates joins if you don't need any columns, but that's not possible > - without a bit of analysis. In the case above everything is simple enough that the planner will certainly collapse everything and it'll be exactly as if you juts wrote the first query. In more complex cases involving LIMIT or GROUP BY etc that may not be true. However there's an underlying question here, what do you mean by "retrieve"? The database always reads the entire row from disk anyways. In fact it reads the whole block that the row is on. If there are large values which have been toasted they're never retrieved unless you actually need their values either for some operation such as a function or operator or because they're in the final output to send to the client. If you mean what is sent over the wire to the client then only the columns listed in the final select list get sent to the client. -- greg http://mit.edu/~gsstark/resume.pdf -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
