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Commit0bd7305

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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
@@ -4893,50 +4893,36 @@ get_rule_expr(Node *node, deparse_context *context,
48934893
CaseWhen*when= (CaseWhen*)lfirst(temp);
48944894
Node*w= (Node*)when->expr;
48954895

4896-
if (!PRETTY_INDENT(context))
4897-
appendStringInfoChar(buf,' ');
4898-
appendContextKeyword(context,"WHEN ",
4899-
0,0,0);
49004896
if (caseexpr->arg)
49014897
{
49024898
/*
4903-
* The parser should have produced WHEN clauses of the
4904-
* form "CaseTestExpr = RHS"; we want to show just the
4905-
*RHS. Iftheuser wrote something silly like "CASE
4906-
*boolexpr WHEN TRUE THEN ...", then the optimizer's
4907-
*simplify_boolean_equality() may have reduced this
4908-
*to just "CaseTestExpr" or "NOT CaseTestExpr", for
4909-
*which we have to show "TRUE" or "FALSE". We have
4910-
*also to consider the possibility that an implicit
4911-
*coercion was inserted between the CaseTestExpr and
4912-
* theoperator.
4899+
* The parser should have produced WHEN clauses of
4900+
*theform "CaseTestExpr = RHS", possibly with an
4901+
*implicit coercion inserted abovetheCaseTestExpr.
4902+
*For accurate decompilation of rules it's essential
4903+
*that we show just the RHS. However in an
4904+
*expression that's been through the optimizer, the
4905+
*WHEN clause could be almost anything (since the
4906+
*equality operator could have been expanded into an
4907+
*inline function). If we don't recognize the form
4908+
*oftheWHEN clause, just punt and display it as-is.
49134909
*/
49144910
if (IsA(w,OpExpr))
49154911
{
49164912
List*args= ((OpExpr*)w)->args;
4917-
Node*rhs;
49184913

4919-
Assert(list_length(args)==2);
4920-
Assert(IsA(strip_implicit_coercions(linitial(args)),
4921-
CaseTestExpr));
4922-
rhs= (Node*)lsecond(args);
4923-
get_rule_expr(rhs,context, false);
4914+
if (list_length(args)==2&&
4915+
IsA(strip_implicit_coercions(linitial(args)),
4916+
CaseTestExpr))
4917+
w= (Node*)lsecond(args);
49244918
}
4925-
elseif (IsA(strip_implicit_coercions(w),
4926-
CaseTestExpr))
4927-
appendStringInfo(buf,"TRUE");
4928-
elseif (not_clause(w))
4929-
{
4930-
Assert(IsA(strip_implicit_coercions((Node*)get_notclausearg((Expr*)w)),
4931-
CaseTestExpr));
4932-
appendStringInfo(buf,"FALSE");
4933-
}
4934-
else
4935-
elog(ERROR,"unexpected CASE WHEN clause: %d",
4936-
(int)nodeTag(w));
49374919
}
4938-
else
4939-
get_rule_expr(w,context, false);
4920+
4921+
if (!PRETTY_INDENT(context))
4922+
appendStringInfoChar(buf,' ');
4923+
appendContextKeyword(context,"WHEN ",
4924+
0,0,0);
4925+
get_rule_expr(w,context, false);
49404926
appendStringInfo(buf," THEN ");
49414927
get_rule_expr((Node*)when->result,context, true);
49424928
}
@@ -4952,6 +4938,19 @@ get_rule_expr(Node *node, deparse_context *context,
49524938
}
49534939
break;
49544940

4941+
caseT_CaseTestExpr:
4942+
{
4943+
/*
4944+
* Normally we should never get here, since for expressions
4945+
* that can contain this node type we attempt to avoid
4946+
* recursing to it. But in an optimized expression we might
4947+
* be unable to avoid that (see comments for CaseExpr). If we
4948+
* do see one, print it as CASE_TEST_EXPR.
4949+
*/
4950+
appendStringInfo(buf,"CASE_TEST_EXPR");
4951+
}
4952+
break;
4953+
49554954
caseT_ArrayExpr:
49564955
{
49574956
ArrayExpr*arrayexpr= (ArrayExpr*)node;

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