Re: [GENERAL] Array assignment behavior (was Re: Stored procedure array limits)

"John D. Burger" <john(at)mitre(dot)org> 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 3 10

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