predtest.c

postgresql8.3.4源码,开源数据库

			list_member_strip(((FuncExpr *) clause)->args, isnullarg) &&
			func_strict(((FuncExpr *) clause)->funcid))
			return true;

		/* foo IS NOT NULL refutes foo IS NULL */
		if (clause && IsA(clause, NullTest) &&
			((NullTest *) clause)->nulltesttype == IS_NOT_NULL &&
			equal(((NullTest *) clause)->arg, isnullarg))
			return true;

		return false;			/* we can't succeed below... */
	}

	/* Try the clause-IS-NULL case */
	if (clause && IsA(clause, NullTest) &&
		((NullTest *) clause)->nulltesttype == IS_NULL)
	{
		Expr	   *isnullarg = ((NullTest *) clause)->arg;

		/* row IS NULL does not act in the simple way we have in mind */
		if (type_is_rowtype(exprType((Node *) isnullarg)))
			return false;

		/* foo IS NULL refutes foo IS NOT NULL */
		if (predicate && IsA(predicate, NullTest) &&
			((NullTest *) predicate)->nulltesttype == IS_NOT_NULL &&
			equal(((NullTest *) predicate)->arg, isnullarg))
			return true;

		return false;			/* we can't succeed below... */
	}

	/* Else try btree operator knowledge */
	return btree_predicate_proof(predicate, clause, true);
}


/*
 * If clause asserts the non-truth of a subclause, return that subclause;
 * otherwise return NULL.
 */
static Node *
extract_not_arg(Node *clause)
{
	if (clause == NULL)
		return NULL;
	if (IsA(clause, BoolExpr))
	{
		BoolExpr   *bexpr = (BoolExpr *) clause;

		if (bexpr->boolop == NOT_EXPR)
			return (Node *) linitial(bexpr->args);
	}
	else if (IsA(clause, BooleanTest))
	{
		BooleanTest *btest = (BooleanTest *) clause;

		if (btest->booltesttype == IS_NOT_TRUE ||
			btest->booltesttype == IS_FALSE ||
			btest->booltesttype == IS_UNKNOWN)
			return (Node *) btest->arg;
	}
	return NULL;
}


/*
 * Check whether an Expr is equal() to any member of a list, ignoring
 * any top-level RelabelType nodes.  This is legitimate for the purposes
 * we use it for (matching IS [NOT] NULL arguments to arguments of strict
 * functions) because RelabelType doesn't change null-ness.  It's helpful
 * for cases such as a varchar argument of a strict function on text.
 */
static bool
list_member_strip(List *list, Expr *datum)
{
	ListCell   *cell;

	if (datum && IsA(datum, RelabelType))
		datum = ((RelabelType *) datum)->arg;

	foreach(cell, list)
	{
		Expr	   *elem = (Expr *) lfirst(cell);

		if (elem && IsA(elem, RelabelType))
			elem = ((RelabelType *) elem)->arg;

		if (equal(elem, datum))
			return true;
	}

	return false;
}


/*
 * Define an "operator implication table" for btree operators ("strategies"),
 * and a similar table for refutation.
 *
 * The strategy numbers defined by btree indexes (see access/skey.h) are:
 *		(1) <	(2) <=	 (3) =	 (4) >=   (5) >
 * and in addition we use (6) to represent <>.	<> is not a btree-indexable
 * operator, but we assume here that if an equality operator of a btree
 * opfamily has a negator operator, the negator behaves as <> for the opfamily.
 *
 * The interpretation of:
 *
 *		test_op = BT_implic_table[given_op-1][target_op-1]
 *
 * where test_op, given_op and target_op are strategy numbers (from 1 to 6)
 * of btree operators, is as follows:
 *
 *	 If you know, for some ATTR, that "ATTR given_op CONST1" is true, and you
 *	 want to determine whether "ATTR target_op CONST2" must also be true, then
 *	 you can use "CONST2 test_op CONST1" as a test.  If this test returns true,
 *	 then the target expression must be true; if the test returns false, then
 *	 the target expression may be false.
 *
 * For example, if clause is "Quantity > 10" and pred is "Quantity > 5"
 * then we test "5 <= 10" which evals to true, so clause implies pred.
 *
 * Similarly, the interpretation of a BT_refute_table entry is:
 *
 *	 If you know, for some ATTR, that "ATTR given_op CONST1" is true, and you
 *	 want to determine whether "ATTR target_op CONST2" must be false, then
 *	 you can use "CONST2 test_op CONST1" as a test.  If this test returns true,
 *	 then the target expression must be false; if the test returns false, then
 *	 the target expression may be true.
 *
 * For example, if clause is "Quantity > 10" and pred is "Quantity < 5"
 * then we test "5 <= 10" which evals to true, so clause refutes pred.
 *
 * An entry where test_op == 0 means the implication cannot be determined.
 */

#define BTLT BTLessStrategyNumber
#define BTLE BTLessEqualStrategyNumber
#define BTEQ BTEqualStrategyNumber
#define BTGE BTGreaterEqualStrategyNumber
#define BTGT BTGreaterStrategyNumber
#define BTNE 6

static const StrategyNumber BT_implic_table[6][6] = {
/*
 *			The target operator:
 *
 *	 LT    LE	 EQ    GE	 GT    NE
 */
	{BTGE, BTGE, 0, 0, 0, BTGE},	/* LT */
	{BTGT, BTGE, 0, 0, 0, BTGT},	/* LE */
	{BTGT, BTGE, BTEQ, BTLE, BTLT, BTNE},		/* EQ */
	{0, 0, 0, BTLE, BTLT, BTLT},	/* GE */
	{0, 0, 0, BTLE, BTLE, BTLE},	/* GT */
	{0, 0, 0, 0, 0, BTEQ}		/* NE */
};

static const StrategyNumber BT_refute_table[6][6] = {
/*
 *			The target operator:
 *
 *	 LT    LE	 EQ    GE	 GT    NE
 */
	{0, 0, BTGE, BTGE, BTGE, 0},	/* LT */
	{0, 0, BTGT, BTGT, BTGE, 0},	/* LE */
	{BTLE, BTLT, BTNE, BTGT, BTGE, BTEQ},		/* EQ */
	{BTLE, BTLT, BTLT, 0, 0, 0},	/* GE */
	{BTLE, BTLE, BTLE, 0, 0, 0},	/* GT */
	{0, 0, BTEQ, 0, 0, 0}		/* NE */
};


/*
 * btree_predicate_proof
 *	  Does the predicate implication or refutation test for a "simple clause"
 *	  predicate and a "simple clause" restriction, when both are simple
 *	  operator clauses using related btree operators.
 *
 * When refute_it == false, we want to prove the predicate true;
 * when refute_it == true, we want to prove the predicate false.
 * (There is enough common code to justify handling these two cases
 * in one routine.)  We return TRUE if able to make the proof, FALSE
 * if not able to prove it.
 *
 * What we look for here is binary boolean opclauses of the form
 * "foo op constant", where "foo" is the same in both clauses.	The operators
 * and constants can be different but the operators must be in the same btree
 * operator family.  We use the above operator implication tables to
 * derive implications between nonidentical clauses.  (Note: "foo" is known
 * immutable, and constants are surely immutable, but we have to check that
 * the operators are too.  As of 8.0 it's possible for opfamilies to contain
 * operators that are merely stable, and we dare not make deductions with
 * these.)
 */
static bool
btree_predicate_proof(Expr *predicate, Node *clause, bool refute_it)
{
	Node	   *leftop,
			   *rightop;
	Node	   *pred_var,
			   *clause_var;
	Const	   *pred_const,
			   *clause_const;
	bool		pred_var_on_left,
				clause_var_on_left,
				pred_op_negated;
	Oid			pred_op,
				clause_op,
				pred_op_negator,
				clause_op_negator,
				test_op = InvalidOid;
	Oid			opfamily_id;
	bool		found = false;
	StrategyNumber pred_strategy,
				clause_strategy,
				test_strategy;
	Oid			clause_righttype;
	Expr	   *test_expr;
	ExprState  *test_exprstate;
	Datum		test_result;
	bool		isNull;
	CatCList   *catlist;
	int			i;
	EState	   *estate;
	MemoryContext oldcontext;

	/*
	 * Both expressions must be binary opclauses with a Const on one side, and
	 * identical subexpressions on the other sides. Note we don't have to
	 * think about binary relabeling of the Const node, since that would have
	 * been folded right into the Const.
	 *
	 * If either Const is null, we also fail right away; this assumes that the
	 * test operator will always be strict.
	 */
	if (!is_opclause(predicate))
		return false;
	leftop = get_leftop(predicate);
	rightop = get_rightop(predicate);
	if (rightop == NULL)
		return false;			/* not a binary opclause */
	if (IsA(rightop, Const))
	{
		pred_var = leftop;
		pred_const = (Const *) rightop;
		pred_var_on_left = true;
	}
	else if (IsA(leftop, Const))
	{
		pred_var = rightop;
		pred_const = (Const *) leftop;
		pred_var_on_left = false;
	}
	else
		return false;			/* no Const to be found */
	if (pred_const->constisnull)
		return false;

	if (!is_opclause(clause))
		return false;
	leftop = get_leftop((Expr *) clause);
	rightop = get_rightop((Expr *) clause);
	if (rightop == NULL)
		return false;			/* not a binary opclause */
	if (IsA(rightop, Const))
	{
		clause_var = leftop;
		clause_const = (Const *) rightop;
		clause_var_on_left = true;
	}
	else if (IsA(leftop, Const))
	{
		clause_var = rightop;
		clause_const = (Const *) leftop;
		clause_var_on_left = false;
	}
	else
		return false;			/* no Const to be found */
	if (clause_const->constisnull)
		return false;

	/*
	 * Check for matching subexpressions on the non-Const sides.  We used to
	 * only allow a simple Var, but it's about as easy to allow any
	 * expression.	Remember we already know that the pred expression does not
	 * contain any non-immutable functions, so identical expressions should
	 * yield identical results.
	 */
	if (!equal(pred_var, clause_var))
		return false;

	/*
	 * Okay, get the operators in the two clauses we're comparing. Commute
	 * them if needed so that we can assume the variables are on the left.
	 */
	pred_op = ((OpExpr *) predicate)->opno;
	if (!pred_var_on_left)
	{
		pred_op = get_commutator(pred_op);
		if (!OidIsValid(pred_op))
			return false;
	}

	clause_op = ((OpExpr *) clause)->opno;
	if (!clause_var_on_left)
	{
		clause_op = get_commutator(clause_op);
		if (!OidIsValid(clause_op))
			return false;
	}

	/*
	 * Try to find a btree opfamily containing the needed operators.
	 *
	 * We must find a btree opfamily that contains both operators, else the
	 * implication can't be determined.  Also, the opfamily must contain a
	 * suitable test operator taking the pred_const and clause_const
	 * datatypes.
	 *
	 * If there are multiple matching opfamilies, assume we can use any one to
	 * determine the logical relationship of the two operators and the correct
	 * corresponding test operator.  This should work for any logically
	 * consistent opfamilies.
	 */
	catlist = SearchSysCacheList(AMOPOPID, 1,
								 ObjectIdGetDatum(pred_op),
								 0, 0, 0);

	/*
	 * If we couldn't find any opfamily containing the pred_op, perhaps it is
	 * a <> operator.  See if it has a negator that is in an opfamily.
	 */
	pred_op_negated = false;
	if (catlist->n_members == 0)
	{
		pred_op_negator = get_negator(pred_op);
		if (OidIsValid(pred_op_negator))
		{
			pred_op_negated = true;
			ReleaseSysCacheList(catlist);
			catlist = SearchSysCacheList(AMOPOPID, 1,
										 ObjectIdGetDatum(pred_op_negator),
										 0, 0, 0);
		}
	}

	/* Also may need the clause_op's negator */
	clause_op_negator = get_negator(clause_op);

	/* Now search the opfamilies */
	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	pred_tuple = &catlist->members[i]->tuple;
		Form_pg_amop pred_form = (Form_pg_amop) GETSTRUCT(pred_tuple);
		HeapTuple	clause_tuple;

		/* Must be btree */
		if (pred_form->amopmethod != BTREE_AM_OID)
			continue;

		/* Get the predicate operator's btree strategy number */
		opfamily_id = pred_form->amopfamily;
		pred_strategy = (StrategyNumber) pred_form->amopstrategy;
		Assert(pred_strategy >= 1 && pred_strategy <= 5);

		if (pred_op_negated)
		{
			/* Only consider negators that are = */
			if (pred_strategy != BTEqualStrategyNumber)
				continue;
			pred_strategy = BTNE;
		}

		/*
		 * From the same opfamily, find a strategy number for the clause_op,
		 * if possible
		 */
		clause_tuple = SearchSysCache(AMOPOPID,
									  ObjectIdGetDatum(clause_op),
									  ObjectIdGetDatum(opfamily_id),
									  0, 0);
		if (HeapTupleIsValid(clause_tuple))
		{
			Form_pg_amop clause_form = (Form_pg_amop) GETSTRUCT(clause_tuple);

			/* Get the restriction clause operator's strategy/datatype */
			clause_strategy = (StrategyNumber) clause_form->amopstrategy;
			Assert(clause_strategy >= 1 && clause_strategy <= 5);
			Assert(clause_form->amoplefttype == pred_form->amoplefttype);
			clause_righttype = clause_form->amoprighttype;
			ReleaseSysCache(clause_tuple);
		}
		else if (OidIsValid(clause_op_negator))
		{
			clause_tuple = SearchSysCache(AMOPOPID,
										  ObjectIdGetDatum(clause_op_negator),
										  ObjectIdGetDatum(opfamily_id),
										  0, 0);
			if (HeapTupleIsValid(clause_tuple))
			{
				Form_pg_amop clause_form = (Form_pg_amop) GETSTRUCT(clause_tuple);

				/* Get the restriction clause operator's strategy/datatype */
				clause_strategy = (StrategyNumber) clause_form->amopstrategy;
				Assert(clause_strategy >= 1 && clause_strategy <= 5);
				Assert(clause_form->amoplefttype == pred_form->amoplefttype);
				clause_righttype = clause_form->amoprighttype;
				ReleaseSysCache(clause_tuple);

				/* Only consider negators that are = */
				if (clause_strategy != BTEqualStrategyNumber)
					continue;
				clause_strategy = BTNE;
			}
			else
				continue;
		}
		else
			continue;

		/*
		 * Look up the "test" strategy number in the implication table
		 */
		if (refute_it)
			test_strategy = BT_refute_table[clause_strategy - 1][pred_strategy - 1];
		else
			test_strategy = BT_implic_table[clause_strategy - 1][pred_strategy - 1];

		if (test_strategy == 0)
		{
			/* Can't determine implication using this interpretation */
			continue;
		}

		/*
		 * See if opfamily has an operator for the test strategy and the
		 * datatypes.
		 */
		if (test_strategy == BTNE)
		{
			test_op = get_opfamily_member(opfamily_id,
										  pred_form->amoprighttype,
										  clause_righttype,
										  BTEqualStrategyNumber);
			if (OidIsValid(test_op))
				test_op = get_negator(test_op);
		}
		else
		{
			test_op = get_opfamily_member(opfamily_id,
										  pred_form->amoprighttype,
										  clause_righttype,
										  test_strategy);
		}
		if (OidIsValid(test_op))
		{
			/*
			 * Last check: test_op must be immutable.
			 *
			 * Note that we require only the test_op to be immutable, not the
			 * original clause_op.	(pred_op is assumed to have been checked
			 * immutable by the caller.)  Essentially we are assuming that the
			 * opfamily is consistent even if it contains operators that are
			 * merely stable.
			 */
			if (op_volatile(test_op) == PROVOLATILE_IMMUTABLE)
			{
				found = true;
				break;
			}
		}
	}

	ReleaseSysCacheList(catlist);

	if (!found)
	{
		/* couldn't find a btree opfamily to interpret the operators */
		return false;
	}

	/*
	 * Evaluate the test.  For this we need an EState.
	 */
	estate = CreateExecutorState();

	/* We can use the estate's working context to avoid memory leaks. */
	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);

	/* Build expression tree */
	test_expr = make_opclause(test_op,
							  BOOLOID,
							  false,
							  (Expr *) pred_const,
							  (Expr *) clause_const);

	/* Prepare it for execution */
	test_exprstate = ExecPrepareExpr(test_expr, estate);

	/* And execute it. */
	test_result = ExecEvalExprSwitchContext(test_exprstate,
											GetPerTupleExprContext(estate),
											&isNull, NULL);

	/* Get back to outer memory context */
	MemoryContextSwitchTo(oldcontext);

	/* Release all the junk we just created */
	FreeExecutorState(estate);

	if (isNull)
	{
		/* Treat a null result as non-proof ... but it's a tad fishy ... */
		elog(DEBUG2, "null predicate test result");
		return false;
	}
	return DatumGetBool(test_result);
}