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Extend the unknowns-are-same-as-known-inputs type resolution heuristic.

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For a very long time, one of the parser's heuristics for resolving
ambiguous operator calls has been to assume that unknown-type literals are
of the same type as the other input (if it's known).  However, this was
only used in the first step of quickly checking for an exact-types match,
and thus did not help in resolving matches that require coercion, such as
matches to polymorphic operators.  As we add more polymorphic operators,
this becomes more of a problem.  This patch adds another use of the same
heuristic as a last-ditch check before failing to resolve an ambiguous
operator or function call.  In particular this will let us define the range
inclusion operator in a less limited way (to come in a follow-on patch).
This commit is contained in:
Tom Lane
2011-11-17 18:28:41 -05:00
parent bf4f96b5e2
commit 1a8b9fb549
2 changed files with 147 additions and 26 deletions
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117
src/backend/parser/parse_func.c
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@ -618,14 +618,16 @@ func_select_candidate(int nargs,
Oid *input_typeids,
FuncCandidateList candidates)
{
FuncCandidateList current_candidate;
FuncCandidateList last_candidate;
FuncCandidateList current_candidate,
first_candidate,
last_candidate;
Oid *current_typeids;
Oid current_type;
int i;
int ncandidates;
int nbestMatch,
nmatch;
nmatch,
nunknowns;
Oid input_base_typeids[FUNC_MAX_ARGS];
TYPCATEGORY slot_category[FUNC_MAX_ARGS],
current_category;
@ -651,9 +653,22 @@ func_select_candidate(int nargs,
* take a domain as an input datatype. Such a function will be selected
* over the base-type function only if it is an exact match at all
* argument positions, and so was already chosen by our caller.
*
* While we're at it, count the number of unknown-type arguments for use
* later.
*/
nunknowns = 0;
for (i = 0; i < nargs; i++)
input_base_typeids[i] = getBaseType(input_typeids[i]);
{
if (input_typeids[i] != UNKNOWNOID)
input_base_typeids[i] = getBaseType(input_typeids[i]);
else
{
/* no need to call getBaseType on UNKNOWNOID */
input_base_typeids[i] = UNKNOWNOID;
nunknowns++;
}
}
/*
* Run through all candidates and keep those with the most matches on
@ -749,14 +764,16 @@ func_select_candidate(int nargs,
return candidates;
/*
* Still too many candidates? Try assigning types for the unknown columns.
* Still too many candidates? Try assigning types for the unknown inputs.
*
* NOTE: for a binary operator with one unknown and one non-unknown input,
* we already tried the heuristic of looking for a candidate with the
* known input type on both sides (see binary_oper_exact()). That's
* essentially a special case of the general algorithm we try next.
*
* We do this by examining each unknown argument position to see if we can
* If there are no unknown inputs, we have no more heuristics that apply,
* and must fail.
*/
if (nunknowns == 0)
return NULL; /* failed to select a best candidate */
/*
* The next step examines each unknown argument position to see if we can
* determine a "type category" for it. If any candidate has an input
* datatype of STRING category, use STRING category (this bias towards
* STRING is appropriate since unknown-type literals look like strings).
@ -770,9 +787,9 @@ func_select_candidate(int nargs,
* Having completed this examination, remove candidates that accept the
* wrong category at any unknown position. Also, if at least one
* candidate accepted a preferred type at a position, remove candidates
* that accept non-preferred types.
*
* If we are down to one candidate at the end, we win.
* that accept non-preferred types. If just one candidate remains,
* return that one. However, if this rule turns out to reject all
* candidates, keep them all instead.
*/
resolved_unknowns = false;
for (i = 0; i < nargs; i++)
@ -835,6 +852,7 @@ func_select_candidate(int nargs,
{
/* Strip non-matching candidates */
ncandidates = 0;
first_candidate = candidates;
last_candidate = NULL;
for (current_candidate = candidates;
current_candidate != NULL;
@ -874,15 +892,78 @@ func_select_candidate(int nargs,
if (last_candidate)
last_candidate->next = current_candidate->next;
else
candidates = current_candidate->next;
first_candidate = current_candidate->next;
}
}
if (last_candidate) /* terminate rebuilt list */
/* if we found any matches, restrict our attention to those */
if (last_candidate)
{
candidates = first_candidate;
/* terminate rebuilt list */
last_candidate->next = NULL;
}
if (ncandidates == 1)
return candidates;
}
if (ncandidates == 1)
return candidates;
/*
* Last gasp: if there are both known- and unknown-type inputs, and all
* the known types are the same, assume the unknown inputs are also that
* type, and see if that gives us a unique match. If so, use that match.
*
* NOTE: for a binary operator with one unknown and one non-unknown input,
* we already tried this heuristic in binary_oper_exact(). However, that
* code only finds exact matches, whereas here we will handle matches that
* involve coercion, polymorphic type resolution, etc.
*/
if (nunknowns < nargs)
{
Oid known_type = UNKNOWNOID;
for (i = 0; i < nargs; i++)
{
if (input_base_typeids[i] == UNKNOWNOID)
continue;
if (known_type == UNKNOWNOID) /* first known arg? */
known_type = input_base_typeids[i];
else if (known_type != input_base_typeids[i])
{
/* oops, not all match */
known_type = UNKNOWNOID;
break;
}
}
if (known_type != UNKNOWNOID)
{
/* okay, just one known type, apply the heuristic */
for (i = 0; i < nargs; i++)
input_base_typeids[i] = known_type;
ncandidates = 0;
last_candidate = NULL;
for (current_candidate = candidates;
current_candidate != NULL;
current_candidate = current_candidate->next)
{
current_typeids = current_candidate->args;
if (can_coerce_type(nargs, input_base_typeids, current_typeids,
COERCION_IMPLICIT))
{
if (++ncandidates > 1)
break; /* not unique, give up */
last_candidate = current_candidate;
}
}
if (ncandidates == 1)
{
/* successfully identified a unique match */
last_candidate->next = NULL;
return last_candidate;
}
}
}
return NULL; /* failed to select a best candidate */
} /* func_select_candidate() */