clauses.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 2,256 行 · 第 1/5 页

	}
	/* It's a simple DISTINCT */
	return false;
}


/*****************************************************************************
 *																			 *
 *		General clause-manipulating routines								 *
 *																			 *
 *****************************************************************************/

/*
 * clause_get_relids_vars
 *	  Retrieves distinct relids and vars appearing within a clause.
 *
 * '*relids' is set to the set of all distinct "varno"s appearing
 *		in Vars within the clause.
 * '*vars' is set to a list of all distinct Vars appearing within the clause.
 *		Var nodes are considered distinct if they have different varno
 *		or varattno values.  If there are several occurrences of the same
 *		varno/varattno, you get a randomly chosen one...
 *
 * Note that upper-level vars are ignored, since they normally will
 * become Params with respect to this query level.
 */
void
clause_get_relids_vars(Node *clause, Relids *relids, List **vars)
{
	List	   *clvars = pull_var_clause(clause, false);
	Relids		varnos = NULL;
	List	   *var_list = NIL;
	List	   *i;

	foreach(i, clvars)
	{
		Var		   *var = (Var *) lfirst(i);
		List	   *vi;

		varnos = bms_add_member(varnos, var->varno);
		foreach(vi, var_list)
		{
			Var		   *in_list = (Var *) lfirst(vi);

			if (in_list->varno == var->varno &&
				in_list->varattno == var->varattno)
				break;
		}
		if (vi == NIL)
			var_list = lcons(var, var_list);
	}
	freeList(clvars);

	*relids = varnos;
	*vars = var_list;
}

/*
 * NumRelids
 *		(formerly clause_relids)
 *
 * Returns the number of different relations referenced in 'clause'.
 */
int
NumRelids(Node *clause)
{
	Relids		varnos = pull_varnos(clause);
	int			result = bms_num_members(varnos);

	bms_free(varnos);
	return result;
}

/*
 * CommuteClause: commute a binary operator clause
 *
 * XXX the clause is destructively modified!
 */
void
CommuteClause(OpExpr *clause)
{
	Oid			opoid;
	Node	   *temp;

	/* Sanity checks: caller is at fault if these fail */
	if (!is_opclause(clause) ||
		length(clause->args) != 2)
		elog(ERROR, "cannot commute non-binary-operator clause");

	opoid = get_commutator(clause->opno);

	if (!OidIsValid(opoid))
		elog(ERROR, "could not find commutator for operator %u",
			 clause->opno);

	/*
	 * modify the clause in-place!
	 */
	clause->opno = opoid;
	clause->opfuncid = InvalidOid;
	/* opresulttype and opretset are assumed not to change */

	temp = lfirst(clause->args);
	lfirst(clause->args) = lsecond(clause->args);
	lsecond(clause->args) = temp;
}


/*--------------------
 * eval_const_expressions
 *
 * Reduce any recognizably constant subexpressions of the given
 * expression tree, for example "2 + 2" => "4".  More interestingly,
 * we can reduce certain boolean expressions even when they contain
 * non-constant subexpressions: "x OR true" => "true" no matter what
 * the subexpression x is.	(XXX We assume that no such subexpression
 * will have important side-effects, which is not necessarily a good
 * assumption in the presence of user-defined functions; do we need a
 * pg_proc flag that prevents discarding the execution of a function?)
 *
 * We do understand that certain functions may deliver non-constant
 * results even with constant inputs, "nextval()" being the classic
 * example.  Functions that are not marked "immutable" in pg_proc
 * will not be pre-evaluated here, although we will reduce their
 * arguments as far as possible.
 *
 * We assume that the tree has already been type-checked and contains
 * only operators and functions that are reasonable to try to execute.
 *--------------------
 */
Node *
eval_const_expressions(Node *node)
{
	/*
	 * The context for the mutator is a list of SQL functions being
	 * recursively simplified, so we start with an empty list.
	 */
	return eval_const_expressions_mutator(node, NIL);
}

static Node *
eval_const_expressions_mutator(Node *node, List *active_fns)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, FuncExpr))
	{
		FuncExpr   *expr = (FuncExpr *) node;
		List	   *args;
		Expr	   *simple;
		FuncExpr   *newexpr;

		/*
		 * Reduce constants in the FuncExpr's arguments.  We know args is
		 * either NIL or a List node, so we can call
		 * expression_tree_mutator directly rather than recursing to self.
		 */
		args = (List *) expression_tree_mutator((Node *) expr->args,
										  eval_const_expressions_mutator,
												(void *) active_fns);

		/*
		 * Code for op/func reduction is pretty bulky, so split it out as
		 * a separate function.
		 */
		simple = simplify_function(expr->funcid, expr->funcresulttype, args,
								   true, active_fns);
		if (simple)				/* successfully simplified it */
			return (Node *) simple;

		/*
		 * The expression cannot be simplified any further, so build and
		 * return a replacement FuncExpr node using the
		 * possibly-simplified arguments.
		 */
		newexpr = makeNode(FuncExpr);
		newexpr->funcid = expr->funcid;
		newexpr->funcresulttype = expr->funcresulttype;
		newexpr->funcretset = expr->funcretset;
		newexpr->funcformat = expr->funcformat;
		newexpr->args = args;
		return (Node *) newexpr;
	}
	if (IsA(node, OpExpr))
	{
		OpExpr	   *expr = (OpExpr *) node;
		List	   *args;
		Expr	   *simple;
		OpExpr	   *newexpr;

		/*
		 * Reduce constants in the OpExpr's arguments.  We know args is
		 * either NIL or a List node, so we can call
		 * expression_tree_mutator directly rather than recursing to self.
		 */
		args = (List *) expression_tree_mutator((Node *) expr->args,
										  eval_const_expressions_mutator,
												(void *) active_fns);

		/*
		 * Need to get OID of underlying function.	Okay to scribble on
		 * input to this extent.
		 */
		set_opfuncid(expr);

		/*
		 * Code for op/func reduction is pretty bulky, so split it out as
		 * a separate function.
		 */
		simple = simplify_function(expr->opfuncid, expr->opresulttype, args,
								   true, active_fns);
		if (simple)				/* successfully simplified it */
			return (Node *) simple;

		/*
		 * The expression cannot be simplified any further, so build and
		 * return a replacement OpExpr node using the possibly-simplified
		 * arguments.
		 */
		newexpr = makeNode(OpExpr);
		newexpr->opno = expr->opno;
		newexpr->opfuncid = expr->opfuncid;
		newexpr->opresulttype = expr->opresulttype;
		newexpr->opretset = expr->opretset;
		newexpr->args = args;
		return (Node *) newexpr;
	}
	if (IsA(node, DistinctExpr))
	{
		DistinctExpr *expr = (DistinctExpr *) node;
		List	   *args;
		List	   *arg;
		bool		has_null_input = false;
		bool		all_null_input = true;
		bool		has_nonconst_input = false;
		Expr	   *simple;
		DistinctExpr *newexpr;

		/*
		 * Reduce constants in the DistinctExpr's arguments.  We know args
		 * is either NIL or a List node, so we can call
		 * expression_tree_mutator directly rather than recursing to self.
		 */
		args = (List *) expression_tree_mutator((Node *) expr->args,
										  eval_const_expressions_mutator,
												(void *) active_fns);

		/*
		 * We must do our own check for NULLs because DistinctExpr has
		 * different results for NULL input than the underlying operator
		 * does.
		 */
		foreach(arg, args)
		{
			if (IsA(lfirst(arg), Const))
			{
				has_null_input |= ((Const *) lfirst(arg))->constisnull;
				all_null_input &= ((Const *) lfirst(arg))->constisnull;
			}
			else
				has_nonconst_input = true;
		}

		/* all constants? then can optimize this out */
		if (!has_nonconst_input)
		{
			/* all nulls? then not distinct */
			if (all_null_input)
				return MAKEBOOLCONST(false, false);

			/* one null? then distinct */
			if (has_null_input)
				return MAKEBOOLCONST(true, false);

			/* otherwise try to evaluate the '=' operator */
			/* (NOT okay to try to inline it, though!) */

			/*
			 * Need to get OID of underlying function.	Okay to scribble
			 * on input to this extent.
			 */
			set_opfuncid((OpExpr *) expr);		/* rely on struct
												 * equivalence */

			/*
			 * Code for op/func reduction is pretty bulky, so split it out
			 * as a separate function.
			 */
			simple = simplify_function(expr->opfuncid, expr->opresulttype,
									   args, false, active_fns);
			if (simple)			/* successfully simplified it */
			{
				/*
				 * Since the underlying operator is "=", must negate its
				 * result
				 */
				Const	   *csimple = (Const *) simple;

				Assert(IsA(csimple, Const));
				csimple->constvalue =
					BoolGetDatum(!DatumGetBool(csimple->constvalue));
				return (Node *) csimple;
			}
		}

		/*
		 * The expression cannot be simplified any further, so build and
		 * return a replacement DistinctExpr node using the
		 * possibly-simplified arguments.
		 */
		newexpr = makeNode(DistinctExpr);
		newexpr->opno = expr->opno;
		newexpr->opfuncid = expr->opfuncid;
		newexpr->opresulttype = expr->opresulttype;
		newexpr->opretset = expr->opretset;
		newexpr->args = args;
		return (Node *) newexpr;
	}
	if (IsA(node, BoolExpr))
	{
		BoolExpr   *expr = (BoolExpr *) node;
		List	   *args;
		Const	   *const_input;

		/*
		 * Reduce constants in the BoolExpr's arguments.  We know args is
		 * either NIL or a List node, so we can call
		 * expression_tree_mutator directly rather than recursing to self.
		 */
		args = (List *) expression_tree_mutator((Node *) expr->args,
										  eval_const_expressions_mutator,
												(void *) active_fns);

		switch (expr->boolop)
		{
			case OR_EXPR:
				{
					/*----------
					 * OR arguments are handled as follows:
					 *	non constant: keep
					 *	FALSE: drop (does not affect result)
					 *	TRUE: force result to TRUE
					 *	NULL: keep only one
					 * We keep one NULL input because ExecEvalOr returns NULL
					 * when no input is TRUE and at least one is NULL.
					 *----------
					 */
					FastList	newargs;
					List	   *arg;
					bool		haveNull = false;
					bool		forceTrue = false;

					FastListInit(&newargs);
					foreach(arg, args)
					{
						if (!IsA(lfirst(arg), Const))
						{
							FastAppend(&newargs, lfirst(arg));
							continue;
						}
						const_input = (Const *) lfirst(arg);
						if (const_input->constisnull)
							haveNull = true;
						else if (DatumGetBool(const_input->constvalue))
							forceTrue = true;
						/* otherwise, we can drop the constant-false input */
					}

					/*
					 * We could return TRUE before falling out of the
					 * loop, but this coding method will be easier to
					 * adapt if we ever add a notion of non-removable
					 * functions. We'd need to check all the inputs for
					 * non-removability.
					 */
					if (forceTrue)
						return MAKEBOOLCONST(true, false);
					if (haveNull)
						FastAppend(&newargs, MAKEBOOLCONST(false, true));
					/* If all the inputs are FALSE, result is FALSE */
					if (FastListValue(&newargs) == NIL)
						return MAKEBOOLCONST(false, false);
					/* If only one nonconst-or-NULL input, it's the result */
					if (lnext(FastListValue(&newargs)) == NIL)
						return (Node *) lfirst(FastListValue(&newargs));
					/* Else we still need an OR node */
					return (Node *) make_orclause(FastListValue(&newargs));
				}
			case AND_EXPR:
				{
					/*----------
					 * AND arguments are handled as follows:
					 *	non constant: keep
					 *	TRUE: drop (does not affect result)
					 *	FALSE: force result to FALSE
					 *	NULL: keep only one
					 * We keep one NULL input because ExecEvalAnd returns NULL
					 * when no input is FALSE and at least one is NULL.
					 *----------
					 */
					FastList	newargs;
					List	   *arg;
					bool		haveNull = false;
					bool		forceFalse = false;

					FastListInit(&newargs);
					foreach(arg, args)
					{
						if (!IsA(lfirst(arg), Const))
						{
							FastAppend(&newargs, lfirst(arg));
							continue;
						}
						const_input = (Const *) lfirst(arg);
						if (const_input->constisnull)
							haveNull = true;
						else if (!DatumGetBool(const_input->constvalue))
							forceFalse = true;
						/* otherwise, we can drop the constant-true input */
					}

					/*
					 * We could return FALSE before falling out of the
					 * loop, but this coding method will be easier to
					 * adapt if we ever add a notion of non-removable
					 * functions. We'd need to check all the inputs for
					 * non-removability.
					 */
					if (forceFalse)
						return MAKEBOOLCONST(false, false);
					if (haveNull)
						FastAppend(&newargs, MAKEBOOLCONST(false, true));
					/* If all the inputs are TRUE, result is TRUE */
					if (FastListValue(&newargs) == NIL)
						return MAKEBOOLCONST(true, false);
					/* If only one nonconst-or-NULL input, it's the result */
					if (lnext(FastListValue(&newargs)) == NIL)
						return (Node *) lfirst(FastListValue(&newargs));
					/* Else we still need an AND node */
					return (Node *) make_andclause(FastListValue(&newargs));
				}
			case NOT_EXPR:
				Assert(length(args) == 1);
				if (IsA(lfirst(args), Const))
				{
					const_input = (Const *) lfirst(args);
					/* NOT NULL => NULL */
					if (const_input->constisnull)
						return MAKEBOOLCONST(false, true);
					/* otherwise pretty easy */
					return MAKEBOOLCONST(!DatumGetBool(const_input->constvalue),
										 false);