On 11 November 2010 16:50, Marko Tiikkaja <marko.tiikk...@cs.helsinki.fi>wrote:
> On 2010-11-11 6:41 PM +0200, David Fetter wrote: > >> On Thu, Nov 11, 2010 at 04:15:34AM +0200, Marko Tiikkaja wrote: >> >>> The discussion around wCTE during the last week or so has brought to >>> my attention that we don't actually have a consensus on how exactly >>> wCTEs should behave. The question seems to be whether or not a >>> statement should see the modifications of statements ran before it. >>> While I think making the modifications visible would be a lot more >>> intuitive, it's not clear how we'd optimize the execution in the >>> future without changing the behaviour (triggers are a big concern). >>> >> >> +1 for letting writeable CTEs see the results of previous CTEs, just >> as current non-writeable ones do. A lot of the useful cases for this >> feature depend on this visibility. >> > > Just to be clear, the main point is whether they see the data modifications > or not. The simplest case to point out this behaviour is: > > WITH t AS (DELETE FROM foo) > SELECT * FROM foo; > > And the big question is: what state of "foo" should the SELECT statement > see? > > I would expect that select to return nothing. And if the user wished to reference what was deleted, they could use RETURNING anyway. </probable ignorance> WITH t AS (UPDATE foo SET col = true) SELECT * FROM foo WHERE col = false; ... Wouldn't this be more practical to have foo's UPDATEs applied prior to SELECT? Otherwise what would the usecase be? -- Thom Brown Twitter: @darkixion IRC (freenode): dark_ixion Registered Linux user: #516935
