2008/9/29 Tom Lane <[EMAIL PROTECTED]>: > Greg Stark <[EMAIL PROTECTED]> writes: >> On 27 Sep 2008, at 09:56 PM, Tom Lane <[EMAIL PROTECTED]> wrote: >>> ISTM that the fundamental problem is that plpgsql doesn't distinguish >>> properly between a null row value (eg, "null::somerowtype") and a >>> row of null values (eg, "row(null,null,...)::somerowtype"). When that >>> code was designed, our main SQL engine was pretty fuzzy about the >>> difference too, but now there is a clear semantic distinction. > >> Iirc the reason for this fuzziness came from the SQL spec definition >> of IS NULL for rows. As long as you maintain that level of spec- >> compliance I don't think there are any other important constraints on >> pg behaviour. > > I started to poke into this and found out that it was a bit subtler than > I thought. It'd be possible to associate a "rowisnull" state value > with a row variable, but the problem is that plpgsql treats the row > fields as independent variables that can be accessed without touching > the row. In particular you can assign null or nonnull values to > individual fields. So consider > > -- presumably, this'll set rowisnull to TRUE: > rowvar := NULL; > -- this had better cause rowisnull to become FALSE: > rowvar.field1 := 42; > -- does this cause it to become TRUE again? > rowvar.field1 := NULL;
this sequence is wrong. in SQL rowvar has same behave as pointer. When you would to fill rowvar you should to call constructor first. some like rowvar := NULL; -- null value rowvar := constructor(null); rowvar := constructor(); rowvar.field = 42; regards Pavel Stehule > > There are a bunch of implementation problems with making any such > behavior happen, since the row field variables don't currently "know" > that they are members of a row, and indeed it's possible for the same > variable to be a member of more than one row. But the core issue is > that this interaction seems to fuzz the distinction between "row is > null" and "all the row's elements are null". In particular, if you > think that rowisnull should be TRUE after the above sequence, then > I think you are saying they are the same thing. So maybe the spec > authors are smarter than we are. > > Thoughts? What would a consistent behavior look like? > > regards, tom lane > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
