clauses.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

			else
				aggtranstypmod = -1;

			avgwidth = get_typavgwidth(aggtranstype, aggtranstypmod);
			avgwidth = MAXALIGN(avgwidth);

			counts->transitionSpace += avgwidth + 2 * sizeof(void *);
		}

		/*
		 * Complain if the aggregate's argument contains any aggregates;
		 * nested agg functions are semantically nonsensical.
		 */
		if (contain_agg_clause((Node *) aggref->target))
			ereport(ERROR,
					(errcode(ERRCODE_GROUPING_ERROR),
					 errmsg("aggregate function calls may not be nested")));

		/*
		 * Having checked that, we need not recurse into the argument.
		 */
		return false;
	}
	Assert(!IsA(node, SubLink));
	return expression_tree_walker(node, count_agg_clauses_walker,
								  (void *) counts);
}


/*****************************************************************************
 *		Support for expressions returning sets
 *****************************************************************************/

/*
 * expression_returns_set
 *	  Test whether an expression returns a set result.
 *
 * Because we use expression_tree_walker(), this can also be applied to
 * whole targetlists; it'll produce TRUE if any one of the tlist items
 * returns a set.
 */
bool
expression_returns_set(Node *clause)
{
	return expression_returns_set_walker(clause, NULL);
}

static bool
expression_returns_set_walker(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, FuncExpr))
	{
		FuncExpr   *expr = (FuncExpr *) node;

		if (expr->funcretset)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, OpExpr))
	{
		OpExpr	   *expr = (OpExpr *) node;

		if (expr->opretset)
			return true;
		/* else fall through to check args */
	}

	/* Avoid recursion for some cases that can't return a set */
	if (IsA(node, Aggref))
		return false;
	if (IsA(node, DistinctExpr))
		return false;
	if (IsA(node, ScalarArrayOpExpr))
		return false;
	if (IsA(node, BoolExpr))
		return false;
	if (IsA(node, SubLink))
		return false;
	if (IsA(node, SubPlan))
		return false;
	if (IsA(node, ArrayExpr))
		return false;
	if (IsA(node, RowExpr))
		return false;
	if (IsA(node, CoalesceExpr))
		return false;
	if (IsA(node, MinMaxExpr))
		return false;
	if (IsA(node, NullIfExpr))
		return false;

	return expression_tree_walker(node, expression_returns_set_walker,
								  context);
}

/*****************************************************************************
 *		Subplan clause manipulation
 *****************************************************************************/

/*
 * contain_subplans
 *	  Recursively search for subplan nodes within a clause.
 *
 * If we see a SubLink node, we will return TRUE.  This is only possible if
 * the expression tree hasn't yet been transformed by subselect.c.  We do not
 * know whether the node will produce a true subplan or just an initplan,
 * but we make the conservative assumption that it will be a subplan.
 *
 * Returns true if any subplan found.
 */
bool
contain_subplans(Node *clause)
{
	return contain_subplans_walker(clause, NULL);
}

static bool
contain_subplans_walker(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, SubPlan) ||
		IsA(node, SubLink))
		return true;			/* abort the tree traversal and return true */
	return expression_tree_walker(node, contain_subplans_walker, context);
}


/*****************************************************************************
 *		Check clauses for mutable functions
 *****************************************************************************/

/*
 * contain_mutable_functions
 *	  Recursively search for mutable functions within a clause.
 *
 * Returns true if any mutable function (or operator implemented by a
 * mutable function) is found.	This test is needed so that we don't
 * mistakenly think that something like "WHERE random() < 0.5" can be treated
 * as a constant qualification.
 *
 * XXX we do not examine sub-selects to see if they contain uses of
 * mutable functions.  It's not real clear if that is correct or not...
 */
bool
contain_mutable_functions(Node *clause)
{
	return contain_mutable_functions_walker(clause, NULL);
}

static bool
contain_mutable_functions_walker(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, FuncExpr))
	{
		FuncExpr   *expr = (FuncExpr *) node;

		if (func_volatile(expr->funcid) != PROVOLATILE_IMMUTABLE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, OpExpr))
	{
		OpExpr	   *expr = (OpExpr *) node;

		if (op_volatile(expr->opno) != PROVOLATILE_IMMUTABLE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, DistinctExpr))
	{
		DistinctExpr *expr = (DistinctExpr *) node;

		if (op_volatile(expr->opno) != PROVOLATILE_IMMUTABLE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, ScalarArrayOpExpr))
	{
		ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) node;

		if (op_volatile(expr->opno) != PROVOLATILE_IMMUTABLE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, NullIfExpr))
	{
		NullIfExpr *expr = (NullIfExpr *) node;

		if (op_volatile(expr->opno) != PROVOLATILE_IMMUTABLE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, SubLink))
	{
		SubLink    *sublink = (SubLink *) node;
		ListCell   *opid;

		foreach(opid, sublink->operOids)
		{
			if (op_volatile(lfirst_oid(opid)) != PROVOLATILE_IMMUTABLE)
				return true;
		}
		/* else fall through to check args */
	}
	return expression_tree_walker(node, contain_mutable_functions_walker,
								  context);
}


/*****************************************************************************
 *		Check clauses for volatile functions
 *****************************************************************************/

/*
 * contain_volatile_functions
 *	  Recursively search for volatile functions within a clause.
 *
 * Returns true if any volatile function (or operator implemented by a
 * volatile function) is found. This test prevents invalid conversions
 * of volatile expressions into indexscan quals.
 *
 * XXX we do not examine sub-selects to see if they contain uses of
 * volatile functions.	It's not real clear if that is correct or not...
 */
bool
contain_volatile_functions(Node *clause)
{
	return contain_volatile_functions_walker(clause, NULL);
}

static bool
contain_volatile_functions_walker(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, FuncExpr))
	{
		FuncExpr   *expr = (FuncExpr *) node;

		if (func_volatile(expr->funcid) == PROVOLATILE_VOLATILE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, OpExpr))
	{
		OpExpr	   *expr = (OpExpr *) node;

		if (op_volatile(expr->opno) == PROVOLATILE_VOLATILE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, DistinctExpr))
	{
		DistinctExpr *expr = (DistinctExpr *) node;

		if (op_volatile(expr->opno) == PROVOLATILE_VOLATILE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, ScalarArrayOpExpr))
	{
		ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) node;

		if (op_volatile(expr->opno) == PROVOLATILE_VOLATILE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, NullIfExpr))
	{
		NullIfExpr *expr = (NullIfExpr *) node;

		if (op_volatile(expr->opno) == PROVOLATILE_VOLATILE)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, SubLink))
	{
		SubLink    *sublink = (SubLink *) node;
		ListCell   *opid;

		foreach(opid, sublink->operOids)
		{
			if (op_volatile(lfirst_oid(opid)) == PROVOLATILE_VOLATILE)
				return true;
		}
		/* else fall through to check args */
	}
	return expression_tree_walker(node, contain_volatile_functions_walker,
								  context);
}


/*****************************************************************************
 *		Check clauses for nonstrict functions
 *****************************************************************************/

/*
 * contain_nonstrict_functions
 *	  Recursively search for nonstrict functions within a clause.
 *
 * Returns true if any nonstrict construct is found --- ie, anything that
 * could produce non-NULL output with a NULL input.
 *
 * The idea here is that the caller has verified that the expression contains
 * one or more Var or Param nodes (as appropriate for the caller's need), and
 * now wishes to prove that the expression result will be NULL if any of these
 * inputs is NULL.	If we return false, then the proof succeeded.
 */
bool
contain_nonstrict_functions(Node *clause)
{
	return contain_nonstrict_functions_walker(clause, NULL);
}

static bool
contain_nonstrict_functions_walker(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, Aggref))
	{
		/* an aggregate could return non-null with null input */
		return true;
	}
	if (IsA(node, ArrayRef))
	{
		/* array assignment is nonstrict */
		if (((ArrayRef *) node)->refassgnexpr != NULL)
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, FuncExpr))
	{
		FuncExpr   *expr = (FuncExpr *) node;

		if (!func_strict(expr->funcid))
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, OpExpr))
	{
		OpExpr	   *expr = (OpExpr *) node;

		if (!op_strict(expr->opno))
			return true;
		/* else fall through to check args */
	}
	if (IsA(node, DistinctExpr))
	{
		/* IS DISTINCT FROM is inherently non-strict */
		return true;
	}
	if (IsA(node, ScalarArrayOpExpr))
	{
		/* inherently non-strict, consider null scalar and empty array */
		return true;
	}
	if (IsA(node, BoolExpr))
	{
		BoolExpr   *expr = (BoolExpr *) node;

		switch (expr->boolop)
		{
			case AND_EXPR:
			case OR_EXPR:
				/* AND, OR are inherently non-strict */
				return true;
			default:
				break;
		}
	}
	if (IsA(node, SubLink))
	{
		/* In some cases a sublink might be strict, but in general not */
		return true;
	}
	if (IsA(node, SubPlan))
		return true;
	if (IsA(node, FieldStore))
		return true;
	if (IsA(node, CaseExpr))
		return true;
	if (IsA(node, CaseWhen))
		return true;
	/* NB: ArrayExpr might someday be nonstrict */
	if (IsA(node, RowExpr))
		return true;
	if (IsA(node, CoalesceExpr))
		return true;
	if (IsA(node, MinMaxExpr))
		return true;
	if (IsA(node, NullIfExpr))
		return true;
	if (IsA(node, NullTest))
		return true;
	if (IsA(node, BooleanTest))
		return true;
	return expression_tree_walker(node, contain_nonstrict_functions_walker,
								  context);
}


/*****************************************************************************
 *		Check for "pseudo-constant" clauses
 *****************************************************************************/

/*
 * is_pseudo_constant_clause
 *	  Detect whether a clause is "constant", ie, it contains no variables
 *	  of the current query level and no uses of volatile functions.
 *	  Such a clause is not necessarily a true constant: it can still contain
 *	  Params and outer-level Vars, not to mention functions whose results
 *	  may vary from one statement to the next.	However, the clause's value
 *	  will be constant over any one scan of the current query, so it can be
 *	  used as an indexscan key or (if a top-level qual) can be pushed up to
 *	  become a gating qual.
 */
bool
is_pseudo_constant_clause(Node *clause)
{
	/*
	 * We could implement this check in one recursive scan.  But since the
	 * check for volatile functions is both moderately expensive and unlikely
	 * to fail, it seems better to look for Vars first and only check for
	 * volatile functions if we find no Vars.
	 */
	if (!contain_var_clause(clause) &&
		!contain_volatile_functions(clause))
		return true;
	return false;
}

/*
 * is_pseudo_constant_clause_relids
 *	  Same as above, except caller already has available the var membership
 *	  of the clause; this lets us avoid the contain_var_clause() scan.
 */
bool
is_pseudo_constant_clause_relids(Node *clause, Relids relids)
{
	if (bms_is_empty(relids) &&
		!contain_volatile_functions(clause))
		return true;
	return false;
}

/*
 * pull_constant_clauses
 *		Scan through a list of qualifications and separate "constant" quals
 *		from those that are not.