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Commit3987e9e

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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
@@ -5187,50 +5187,36 @@ get_rule_expr(Node *node, deparse_context *context,
51875187
CaseWhen*when= (CaseWhen*)lfirst(temp);
51885188
Node*w= (Node*)when->expr;
51895189

5190-
if (!PRETTY_INDENT(context))
5191-
appendStringInfoChar(buf,' ');
5192-
appendContextKeyword(context,"WHEN ",
5193-
0,0,0);
51945190
if (caseexpr->arg)
51955191
{
51965192
/*
5197-
* The parser should have produced WHEN clauses of the
5198-
* form "CaseTestExpr = RHS"; we want to show just the
5199-
*RHS. Iftheuser wrote something silly like "CASE
5200-
*boolexpr WHEN TRUE THEN ...", then the optimizer's
5201-
*simplify_boolean_equality() may have reduced this
5202-
*to just "CaseTestExpr" or "NOT CaseTestExpr", for
5203-
*which we have to show "TRUE" or "FALSE". We have
5204-
*also to consider the possibility that an implicit
5205-
*coercion was inserted between the CaseTestExpr and
5206-
* theoperator.
5193+
* The parser should have produced WHEN clauses of
5194+
*theform "CaseTestExpr = RHS", possibly with an
5195+
*implicit coercion inserted abovetheCaseTestExpr.
5196+
*For accurate decompilation of rules it's essential
5197+
*that we show just the RHS. However in an
5198+
*expression that's been through the optimizer, the
5199+
*WHEN clause could be almost anything (since the
5200+
*equality operator could have been expanded into an
5201+
*inline function). If we don't recognize the form
5202+
*oftheWHEN clause, just punt and display it as-is.
52075203
*/
52085204
if (IsA(w,OpExpr))
52095205
{
52105206
List*args= ((OpExpr*)w)->args;
5211-
Node*rhs;
52125207

5213-
Assert(list_length(args)==2);
5214-
Assert(IsA(strip_implicit_coercions(linitial(args)),
5215-
CaseTestExpr));
5216-
rhs= (Node*)lsecond(args);
5217-
get_rule_expr(rhs,context, false);
5208+
if (list_length(args)==2&&
5209+
IsA(strip_implicit_coercions(linitial(args)),
5210+
CaseTestExpr))
5211+
w= (Node*)lsecond(args);
52185212
}
5219-
elseif (IsA(strip_implicit_coercions(w),
5220-
CaseTestExpr))
5221-
appendStringInfo(buf,"TRUE");
5222-
elseif (not_clause(w))
5223-
{
5224-
Assert(IsA(strip_implicit_coercions((Node*)get_notclausearg((Expr*)w)),
5225-
CaseTestExpr));
5226-
appendStringInfo(buf,"FALSE");
5227-
}
5228-
else
5229-
elog(ERROR,"unexpected CASE WHEN clause: %d",
5230-
(int)nodeTag(w));
52315213
}
5232-
else
5233-
get_rule_expr(w,context, false);
5214+
5215+
if (!PRETTY_INDENT(context))
5216+
appendStringInfoChar(buf,' ');
5217+
appendContextKeyword(context,"WHEN ",
5218+
0,0,0);
5219+
get_rule_expr(w,context, false);
52345220
appendStringInfo(buf," THEN ");
52355221
get_rule_expr((Node*)when->result,context, true);
52365222
}
@@ -5246,6 +5232,19 @@ get_rule_expr(Node *node, deparse_context *context,
52465232
}
52475233
break;
52485234

5235+
caseT_CaseTestExpr:
5236+
{
5237+
/*
5238+
* Normally we should never get here, since for expressions
5239+
* that can contain this node type we attempt to avoid
5240+
* recursing to it. But in an optimized expression we might
5241+
* be unable to avoid that (see comments for CaseExpr). If we
5242+
* do see one, print it as CASE_TEST_EXPR.
5243+
*/
5244+
appendStringInfo(buf,"CASE_TEST_EXPR");
5245+
}
5246+
break;
5247+
52495248
caseT_ArrayExpr:
52505249
{
52515250
ArrayExpr*arrayexpr= (ArrayExpr*)node;

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