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Fix "cannot accept a set" error when only some arms of a CASE return a set.

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In commit c1352052ef, I implemented an
optimization that assumed that a function's argument expressions would
either always return a set (ie multiple rows), or always not.  This is
wrong however: we allow CASE expressions in which some arms return a set
of some type and others just return a scalar of that type.  There may be
other examples as well.  To fix, replace the run-time test of whether an
argument returned a set with a static precheck (expression_returns_set).
This adds a little bit of query startup overhead, but it seems barely
measurable.

Per bug #8228 from David Johnston.  This has been broken since 8.0,
so patch all supported branches.
This commit is contained in:
Tom Lane
2014-01-08 20:18:06 -05:00
parent daa7527afc
commit 080b7db72e
3 changed files with 61 additions and 17 deletions
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55
src/backend/executor/execQual.c
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@ -1634,9 +1634,7 @@ tupledesc_match(TupleDesc dst_tupdesc, TupleDesc src_tupdesc)
* init_fcache is presumed already run on the FuncExprState.
*
* This function handles the most general case, wherein the function or
* one of its arguments might (or might not) return a set. If we find
* no sets involved, we will change the FuncExprState's function pointer
* to use a simpler method on subsequent calls.
* one of its arguments can return a set.
*/
static Datum
ExecMakeFunctionResult(FuncExprState *fcache,
@ -1906,13 +1904,12 @@ restart:
/*
* Non-set case: much easier.
*
* We change the ExprState function pointer to use the simpler
* ExecMakeFunctionResultNoSets on subsequent calls. This amounts to
* assuming that no argument can return a set if it didn't do so the
* first time.
* In common cases, this code path is unreachable because we'd have
* selected ExecMakeFunctionResultNoSets instead. However, it's
* possible to get here if an argument sometimes produces set results
* and sometimes scalar results. For example, a CASE expression might
* call a set-returning function in only some of its arms.
*/
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResultNoSets;
if (isDone)
*isDone = ExprSingleResult;
@ -2371,10 +2368,22 @@ ExecEvalFunc(FuncExprState *fcache,
init_fcache(func->funcid, func->inputcollid, fcache,
econtext->ecxt_per_query_memory, true);
/* Go directly to ExecMakeFunctionResult on subsequent uses */
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
/*
* We need to invoke ExecMakeFunctionResult if either the function itself
* or any of its input expressions can return a set. Otherwise, invoke
* ExecMakeFunctionResultNoSets. In either case, change the evalfunc
* pointer to go directly there on subsequent uses.
*/
if (fcache->func.fn_retset || expression_returns_set((Node *) func->args))
{
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
}
else
{
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResultNoSets;
return ExecMakeFunctionResultNoSets(fcache, econtext, isNull, isDone);
}
}
/* ----------------------------------------------------------------
@ -2394,10 +2403,22 @@ ExecEvalOper(FuncExprState *fcache,
init_fcache(op->opfuncid, op->inputcollid, fcache,
econtext->ecxt_per_query_memory, true);
/* Go directly to ExecMakeFunctionResult on subsequent uses */
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
/*
* We need to invoke ExecMakeFunctionResult if either the function itself
* or any of its input expressions can return a set. Otherwise, invoke
* ExecMakeFunctionResultNoSets. In either case, change the evalfunc
* pointer to go directly there on subsequent uses.
*/
if (fcache->func.fn_retset || expression_returns_set((Node *) op->args))
{
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
}
else
{
fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResultNoSets;
return ExecMakeFunctionResultNoSets(fcache, econtext, isNull, isDone);
}
}
/* ----------------------------------------------------------------