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Commit97a39f2

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Fix "cannot accept a set" error when only some arms of a CASE return a set.
In commitc135205, I implemented anoptimization that assumed that a function's argument expressions wouldeither always return a set (ie multiple rows), or always not. This iswrong however: we allow CASE expressions in which some arms return a setof some type and others just return a scalar of that type. There may beother examples as well. To fix, replace the run-time test of whether anargument returned a set with a static precheck (expression_returns_set).This adds a little bit of query startup overhead, but it seems barelymeasurable.Per bug #8228 from David Johnston. This has been broken since 8.0,so patch all supported branches.
1 parent3bd8987 commit97a39f2

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3 files changed

+61
-17
lines changed

3 files changed

+61
-17
lines changed

‎src/backend/executor/execQual.c‎

Lines changed: 38 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -1631,9 +1631,7 @@ tupledesc_match(TupleDesc dst_tupdesc, TupleDesc src_tupdesc)
16311631
* init_fcache is presumed already run on the FuncExprState.
16321632
*
16331633
* This function handles the most general case, wherein the function or
1634-
* one of its arguments might (or might not) return a set.If we find
1635-
* no sets involved, we will change the FuncExprState's function pointer
1636-
* to use a simpler method on subsequent calls.
1634+
* one of its arguments can return a set.
16371635
*/
16381636
staticDatum
16391637
ExecMakeFunctionResult(FuncExprState*fcache,
@@ -1895,13 +1893,12 @@ ExecMakeFunctionResult(FuncExprState *fcache,
18951893
/*
18961894
* Non-set case: much easier.
18971895
*
1898-
* We change the ExprState function pointer to use the simpler
1899-
* ExecMakeFunctionResultNoSets on subsequent calls. This amounts to
1900-
* assuming that no argument can return a set if it didn't do so the
1901-
* first time.
1896+
* In common cases, this code path is unreachable because we'd have
1897+
* selected ExecMakeFunctionResultNoSets instead. However, it's
1898+
* possible to get here if an argument sometimes produces set results
1899+
* and sometimes scalar results. For example, a CASE expression might
1900+
* call a set-returning function in only some of its arms.
19021901
*/
1903-
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResultNoSets;
1904-
19051902
if (isDone)
19061903
*isDone=ExprSingleResult;
19071904

@@ -2360,10 +2357,22 @@ ExecEvalFunc(FuncExprState *fcache,
23602357
init_fcache(func->funcid,func->inputcollid,fcache,
23612358
econtext->ecxt_per_query_memory, true);
23622359

2363-
/* Go directly to ExecMakeFunctionResult on subsequent uses */
2364-
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResult;
2365-
2366-
returnExecMakeFunctionResult(fcache,econtext,isNull,isDone);
2360+
/*
2361+
* We need to invoke ExecMakeFunctionResult if either the function itself
2362+
* or any of its input expressions can return a set. Otherwise, invoke
2363+
* ExecMakeFunctionResultNoSets. In either case, change the evalfunc
2364+
* pointer to go directly there on subsequent uses.
2365+
*/
2366+
if (fcache->func.fn_retset||expression_returns_set((Node*)func->args))
2367+
{
2368+
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResult;
2369+
returnExecMakeFunctionResult(fcache,econtext,isNull,isDone);
2370+
}
2371+
else
2372+
{
2373+
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResultNoSets;
2374+
returnExecMakeFunctionResultNoSets(fcache,econtext,isNull,isDone);
2375+
}
23672376
}
23682377

23692378
/* ----------------------------------------------------------------
@@ -2383,10 +2392,22 @@ ExecEvalOper(FuncExprState *fcache,
23832392
init_fcache(op->opfuncid,op->inputcollid,fcache,
23842393
econtext->ecxt_per_query_memory, true);
23852394

2386-
/* Go directly to ExecMakeFunctionResult on subsequent uses */
2387-
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResult;
2388-
2389-
returnExecMakeFunctionResult(fcache,econtext,isNull,isDone);
2395+
/*
2396+
* We need to invoke ExecMakeFunctionResult if either the function itself
2397+
* or any of its input expressions can return a set. Otherwise, invoke
2398+
* ExecMakeFunctionResultNoSets. In either case, change the evalfunc
2399+
* pointer to go directly there on subsequent uses.
2400+
*/
2401+
if (fcache->func.fn_retset||expression_returns_set((Node*)op->args))
2402+
{
2403+
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResult;
2404+
returnExecMakeFunctionResult(fcache,econtext,isNull,isDone);
2405+
}
2406+
else
2407+
{
2408+
fcache->xprstate.evalfunc= (ExprStateEvalFunc)ExecMakeFunctionResultNoSets;
2409+
returnExecMakeFunctionResultNoSets(fcache,econtext,isNull,isDone);
2410+
}
23902411
}
23912412

23922413
/* ----------------------------------------------------------------

‎src/test/regress/expected/rangefuncs.out‎

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -930,3 +930,17 @@ select * from foobar(); -- fail
930930
ERROR: function return row and query-specified return row do not match
931931
DETAIL: Returned row contains 3 attributes, but query expects 2.
932932
drop function foobar();
933+
-- check behavior when a function's input sometimes returns a set (bug #8228)
934+
SELECT *,
935+
lower(CASE WHEN id = 2 THEN (regexp_matches(str, '^0*([1-9]\d+)$'))[1]
936+
ELSE str
937+
END)
938+
FROM
939+
(VALUES (1,''), (2,'0000000049404'), (3,'FROM 10000000876')) v(id, str);
940+
id | str | lower
941+
----+------------------+------------------
942+
1 | |
943+
2 | 0000000049404 | 49404
944+
3 | FROM 10000000876 | from 10000000876
945+
(3 rows)
946+

‎src/test/regress/sql/rangefuncs.sql‎

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -455,3 +455,12 @@ $$ select (1, 2.1, 3) $$ language sql;
455455
select*from foobar();-- fail
456456

457457
dropfunction foobar();
458+
459+
-- check behavior when a function's input sometimes returns a set (bug #8228)
460+
461+
SELECT*,
462+
lower(CASE WHEN id=2 THEN (regexp_matches(str,'^0*([1-9]\d+)$'))[1]
463+
ELSE str
464+
END)
465+
FROM
466+
(VALUES (1,''), (2,'0000000049404'), (3,'FROM 10000000876')) v(id, str);

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