clauses.c

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

		/* 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, CoalesceExpr))
		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;
		List	   *opid;

		foreach(opid, sublink->operOids)
		{
			if (op_volatile(lfirsto(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;
		List	   *opid;

		foreach(opid, sublink->operOids)
		{
			if (op_volatile(lfirsto(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.
 *
 * XXX we do not examine sub-selects to see if they contain uses of
 * nonstrict functions. It's not real clear if that is correct or not...
 * for the current usage it does not matter, since inline_function()
 * rejects cases with sublinks.
 */
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, 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 OR_EXPR:
			case AND_EXPR:
				/* OR, AND are inherently non-strict */
				return true;
			default:
				break;
		}
	}
	if (IsA(node, CaseExpr))
		return true;
	/* NB: ArrayExpr might someday be nonstrict */
	if (IsA(node, CoalesceExpr))
		return true;
	if (IsA(node, NullIfExpr))
		return true;
	if (IsA(node, NullTest))
		return true;
	if (IsA(node, BooleanTest))
		return true;
	if (IsA(node, SubLink))
	{
		SubLink    *sublink = (SubLink *) node;
		List	   *opid;

		foreach(opid, sublink->operOids)
		{
			if (!op_strict(lfirsto(opid)))
				return true;
		}
		/* else fall through to check args */
	}
	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;
}

/*
 * pull_constant_clauses
 *		Scan through a list of qualifications and separate "constant" quals
 *		from those that are not.
 *
 * Returns a list of the pseudo-constant clauses in constantQual and the
 * remaining quals as the return value.
 */
List *
pull_constant_clauses(List *quals, List **constantQual)
{
	FastList	constqual,
				restqual;
	List	   *q;

	FastListInit(&constqual);
	FastListInit(&restqual);

	foreach(q, quals)
	{
		Node	   *qual = (Node *) lfirst(q);

		if (is_pseudo_constant_clause(qual))
			FastAppend(&constqual, qual);
		else
			FastAppend(&restqual, qual);
	}
	*constantQual = FastListValue(&constqual);
	return FastListValue(&restqual);
}


/*****************************************************************************
 *		Tests on clauses of queries
 *
 * Possibly this code should go someplace else, since this isn't quite the
 * same meaning of "clause" as is used elsewhere in this module.  But I can't
 * think of a better place for it...
 *****************************************************************************/

/*
 * Test whether a query uses DISTINCT ON, ie, has a distinct-list that is
 * not the same as the set of output columns.
 */
bool
has_distinct_on_clause(Query *query)
{
	List	   *targetList;

	/* Is there a DISTINCT clause at all? */
	if (query->distinctClause == NIL)
		return false;

	/*
	 * If the DISTINCT list contains all the nonjunk targetlist items, and
	 * nothing else (ie, no junk tlist items), then it's a simple
	 * DISTINCT, else it's DISTINCT ON.  We do not require the lists to be
	 * in the same order (since the parser may have adjusted the DISTINCT
	 * clause ordering to agree with ORDER BY).  Furthermore, a
	 * non-DISTINCT junk tlist item that is in the sortClause is also
	 * evidence of DISTINCT ON, since we don't allow ORDER BY on junk
	 * tlist items when plain DISTINCT is used.
	 *
	 * This code assumes that the DISTINCT list is valid, ie, all its entries
	 * match some entry of the tlist.
	 */
	foreach(targetList, query->targetList)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(targetList);

		if (tle->resdom->ressortgroupref == 0)
		{
			if (tle->resdom->resjunk)
				continue;		/* we can ignore unsorted junk cols */
			return true;		/* definitely not in DISTINCT list */
		}
		if (targetIsInSortList(tle, query->distinctClause))
		{
			if (tle->resdom->resjunk)
				return true;	/* junk TLE in DISTINCT means DISTINCT ON */
			/* else this TLE is okay, keep looking */
		}
		else
		{
			/* This TLE is not in DISTINCT list */
			if (!tle->resdom->resjunk)
				return true;	/* non-junk, non-DISTINCT, so DISTINCT ON */
			if (targetIsInSortList(tle, query->sortClause))
				return true;	/* sorted, non-distinct junk */
			/* unsorted junk is okay, keep looking */
		}