Re: [HACKERS] [GENERAL] Array assignment behavior (was Re: [ADMIN] Stored procedure array limits)
On Sep 29, 2006, at 9:14 AM, Tom Lane wrote: [ expanding this thread, as it now needs wider discussion ] Paul B. Anderson [EMAIL PROTECTED] writes: Actually, I was not filling all of the arrays in sequential order. I added code to initialize them in order and the function seems to be working now. Is that a known problem? Well, it's a documented behavior: section 8.10.4 saith A stored array value can be enlarged by assigning to an element adjacent to those already present, or by assigning to a slice that is adjacent to or overlaps the data already present. Up to 8.2 we didn't have a lot of choice about this, because without any ability to have nulls embedded in arrays, there wasn't any sane thing to do with the intermediate positions if you assigned to an element not adjacent to the existing range. As of 8.2 we could allow assignment to arbitrary positions by filling the intermediate positions with nulls. The code hasn't actually been changed to allow that, but it's something we could consider doing now. Comments? At first blush, this strikes me as a bit too magical/implicit. Are there other languages where sequences behave similarly? The best analogy that comes to mind is sparse files, but in that case there is an implicit contract that the intervening empty regions do not actually occupy physical space, doesn't sound like that's true here. I think the result of this change would be more difficult debugging of off-by-one errors and their ilk, rather than actually being a real benefit. OTOH, perhaps there is a real use-case I am missing here. I don't see the rest of this thread on GENERAL and I couldn't find it searching the archives, where did it come from? -Casey ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] [GENERAL] Array assignment behavior (was Re: [ADMIN] Stored procedure array limits)
As of 8.2 we could allow assignment to arbitrary positions by filling the intermediate positions with nulls. The code hasn't actually been changed to allow that, but it's something we could consider doing now. At first blush, this strikes me as a bit too magical/implicit. Are there other languages where sequences behave similarly? perl -e '@A = (1, 2, 3); print @A\n; $A[10] = 10; print @A\n;' 1 2 3 1 2 310 - John D. Burger MITRE ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] [GENERAL] Array assignment behavior (was Re: [ADMIN] Stored procedure array limits)
John D. Burger [EMAIL PROTECTED] writes: As of 8.2 we could allow assignment to arbitrary positions by filling the intermediate positions with nulls. The code hasn't actually been changed to allow that, but it's something we could consider doing now. At first blush, this strikes me as a bit too magical/implicit. Are there other languages where sequences behave similarly? perl -e '@A = (1, 2, 3); print @A\n; $A[10] = 10; print @A\n;' 1 2 3 1 2 310 Actually, now that I look closely, I think the SQL spec demands exactly this. Recall that SQL99 only allows one-dimensional, lower-bound-one arrays. The specification for UPDATE ... SET C[I] = SV ... reads Case: i) If the value of C is null, then an exception condition is raised: data exception - null value in array target. ii) Otherwise: 1) Let N be the maximum cardinality of C. 2) Let M be the cardinality of the value of C. 3) Let I be the value of the simple value specification immediately contained in update target. 4) Let EDT be the element type of C. 5) Case: A) If I is greater than zero and less than or equal to M, then the value of C is replaced by an array A with element type EDT and cardinality M derived as follows: I) For j varying from 1 (one) to I-1 and from I+1 to M, the j-th element in A is the value of the j-th element in C. II) The I-th element of A is set to the specified update value, denoted by SV, by applying the General Rules of Subclause 9.2, Store assignment, to the I-th element of A and SV as TARGET and VALUE, respectively. B) If I is greater than M and less than or equal to N, then the value of C is replaced by an array A with element type EDT and cardinality I derived as follows: I) For j varying from 1 (one) to M, the j-th element in A is the value of the j-th element in C. II) For j varying from M+1 to I-1, the j-th element in A is the null value. III) The I-th element of A is set to the specified update value, denoted by SV, by applying the General Rules of Subclause 9.2, Store assignment, to the I-th element of A and SV as TARGET and VALUE, respectively. C) Otherwise, an exception condition is raised: data exception - array element error. We currently violate case i by allowing the null array value to be replaced by a single-element array. I'm disinclined to change that, as I think our behavior is more useful than the spec's. But case ii.5.B pretty clearly describes null-fill, so I think we'd better do that, now that we can. regards, tom lane ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
