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Commit6d24189

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Make decompilation of optimized CASE constructs more robust.
We had some hacks in ruleutils.c to cope with various odd transformationsthat the optimizer could do on a CASE foo WHEN "CaseTestExpr = RHS" clause.However, the fundamental impossibility of covering all cases was exposedby Heikki, who pointed out that the "=" operator could get replaced by aninlined SQL function, which could contain nearly anything at all. So giveup on the hacks and just print the expression as-is if we fail to recognizeit as "CaseTestExpr = RHS". (We must cover that case so that decompiledrules print correctly; but we are not under any obligation to make EXPLAINoutput be 100% valid SQL in all cases, and already could not do so in someother cases.) This approach requires that we have some printablerepresentation of the CaseTestExpr node type; I used "CASE_TEST_EXPR".Back-patch to all supported branches, since the problem case fails in all.
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‎src/backend/utils/adt/ruleutils.c

Lines changed: 33 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -3678,50 +3678,36 @@ get_rule_expr(Node *node, deparse_context *context,
36783678
CaseWhen*when= (CaseWhen*)lfirst(temp);
36793679
Node*w= (Node*)when->expr;
36803680

3681-
if (!PRETTY_INDENT(context))
3682-
appendStringInfoChar(buf,' ');
3683-
appendContextKeyword(context,"WHEN ",
3684-
0,0,0);
36853681
if (caseexpr->arg)
36863682
{
36873683
/*
3688-
* The parser should have produced WHEN clauses of the
3689-
* form "CaseTestExpr = RHS"; we want to show just the
3690-
*RHS. Iftheuser wrote something silly like "CASE
3691-
*boolexpr WHEN TRUE THEN ...", then the optimizer's
3692-
*simplify_boolean_equality() may have reduced this
3693-
*to just "CaseTestExpr" or "NOT CaseTestExpr", for
3694-
*which we have to show "TRUE" or "FALSE". We have
3695-
*also to consider the possibility that an implicit
3696-
*coercion was inserted between the CaseTestExpr and
3697-
* theoperator.
3684+
* The parser should have produced WHEN clauses of
3685+
*theform "CaseTestExpr = RHS", possibly with an
3686+
*implicit coercion inserted abovetheCaseTestExpr.
3687+
*For accurate decompilation of rules it's essential
3688+
*that we show just the RHS. However in an
3689+
*expression that's been through the optimizer, the
3690+
*WHEN clause could be almost anything (since the
3691+
*equality operator could have been expanded into an
3692+
*inline function). If we don't recognize the form
3693+
*oftheWHEN clause, just punt and display it as-is.
36983694
*/
36993695
if (IsA(w,OpExpr))
37003696
{
37013697
List*args= ((OpExpr*)w)->args;
3702-
Node*rhs;
37033698

3704-
Assert(list_length(args)==2);
3705-
Assert(IsA(strip_implicit_coercions(linitial(args)),
3706-
CaseTestExpr));
3707-
rhs= (Node*)lsecond(args);
3708-
get_rule_expr(rhs,context, false);
3699+
if (list_length(args)==2&&
3700+
IsA(strip_implicit_coercions(linitial(args)),
3701+
CaseTestExpr))
3702+
w= (Node*)lsecond(args);
37093703
}
3710-
elseif (IsA(strip_implicit_coercions(w),
3711-
CaseTestExpr))
3712-
appendStringInfo(buf,"TRUE");
3713-
elseif (not_clause(w))
3714-
{
3715-
Assert(IsA(strip_implicit_coercions((Node*)get_notclausearg((Expr*)w)),
3716-
CaseTestExpr));
3717-
appendStringInfo(buf,"FALSE");
3718-
}
3719-
else
3720-
elog(ERROR,"unexpected CASE WHEN clause: %d",
3721-
(int)nodeTag(w));
37223704
}
3723-
else
3724-
get_rule_expr(w,context, false);
3705+
3706+
if (!PRETTY_INDENT(context))
3707+
appendStringInfoChar(buf,' ');
3708+
appendContextKeyword(context,"WHEN ",
3709+
0,0,0);
3710+
get_rule_expr(w,context, false);
37253711
appendStringInfo(buf," THEN ");
37263712
get_rule_expr((Node*)when->result,context, true);
37273713
}
@@ -3737,6 +3723,19 @@ get_rule_expr(Node *node, deparse_context *context,
37373723
}
37383724
break;
37393725

3726+
caseT_CaseTestExpr:
3727+
{
3728+
/*
3729+
* Normally we should never get here, since for expressions
3730+
* that can contain this node type we attempt to avoid
3731+
* recursing to it. But in an optimized expression we might
3732+
* be unable to avoid that (see comments for CaseExpr). If we
3733+
* do see one, print it as CASE_TEST_EXPR.
3734+
*/
3735+
appendStringInfo(buf,"CASE_TEST_EXPR");
3736+
}
3737+
break;
3738+
37403739
caseT_ArrayExpr:
37413740
{
37423741
ArrayExpr*arrayexpr= (ArrayExpr*)node;

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