Re: [PATCH] Implement INSERT SET syntax

David Steele <david(at)pgmasters(dot)net> writes:
> On 12/3/19 4:44 AM, Gareth Palmer wrote:
>> Attached is a fixed version.

> Does this version of the patch address your concerns?

No. I still find the reliance on a FROM clause being present
to be pretty arbitrary. Also, I don't believe that ruleutils.c
requires no changes, because it's not going to be possible to
transform every usage of this syntax to old-style. I tried to
prove the point with this trivial example:

regression=# create table foo (f1 int ,f2 int, f3 int);
CREATE TABLE
regression=# create table bar (f1 int ,f2 int, f3 int);
CREATE TABLE
regression=# create rule r1 as on insert to foo do instead
regression-# insert into bar set (f1,f2,f3) = (select f1,f2,f3 from foo);

intending to show that the rule decompilation was bogus, but
I didn't get that far because the parser crashed:

TRAP: FailedAssertion("pstate->p_multiassign_exprs == NIL", File: "parse_target.c", Line: 287)
postgres: postgres regression [local] CREATE RULE(ExceptionalCondition+0x55)[0x8fb6e5]
postgres: postgres regression [local] CREATE RULE[0x5bd0c3]
postgres: postgres regression [local] CREATE RULE[0x583def]
postgres: postgres regression [local] CREATE RULE(transformStmt+0x2d5)[0x582665]
postgres: postgres regression [local] CREATE RULE(transformRuleStmt+0x2ad)[0x5bf2ad]
postgres: postgres regression [local] CREATE RULE(DefineRule+0x17)[0x793847]

If I do it like this, I get a different assertion:

regression=# insert into bar set (f1,f2,f3) = (select f1,f2,f3) from foo;
server closed the connection unexpectedly

TRAP: FailedAssertion("exprKind == EXPR_KIND_UPDATE_SOURCE", File: "parse_target.c", Line: 209)
postgres: postgres regression [local] INSERT(ExceptionalCondition+0x55)[0x8fb6e5]
postgres: postgres regression [local] INSERT(transformTargetList+0x1a7)[0x5bd277]
postgres: postgres regression [local] INSERT(transformStmt+0xbe0)[0x582f70]
postgres: postgres regression [local] INSERT[0x5839f3]
postgres: postgres regression [local] INSERT(transformStmt+0x2d5)[0x582665]
postgres: postgres regression [local] INSERT(transformTopLevelStmt+0xd)[0x58411d]
postgres: postgres regression [local] INSERT(parse_analyze+0x69)[0x584269]

No doubt that's all fixable, but the realization that some cases of
this syntax are *not* just syntactic sugar for standards-compliant
syntax is giving me pause. Do we really want to get out front of
the SQL committee on extending INSERT in an incompatible way?

regards, tom lane