clauses.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

 *
 * 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)
{
	List	   *constqual = NIL,
			   *restqual = NIL;
	ListCell   *q;

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

		if (is_pseudo_constant_clause(qual))
			constqual = lappend(constqual, qual);
		else
			restqual = lappend(restqual, qual);
	}
	*constantQual = constqual;
	return 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)
{
	ListCell   *l;

	/* 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(l, query->targetList)
	{
		TargetEntry *tle = (TargetEntry *) lfirst(l);

		if (tle->ressortgroupref == 0)
		{
			if (tle->resjunk)
				continue;		/* we can ignore unsorted junk cols */
			return true;		/* definitely not in DISTINCT list */
		}
		if (targetIsInSortList(tle, query->distinctClause))
		{
			if (tle->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->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 */
		}
	}
	/* It's a simple DISTINCT */
	return false;
}

/*
 * Test whether a query uses simple DISTINCT, ie, has a distinct-list that
 * is the same as the set of output columns.
 */
bool
has_distinct_clause(Query *query)
{
	/* Is there a DISTINCT clause at all? */
	if (query->distinctClause == NIL)
		return false;

	/* It's DISTINCT if it's not DISTINCT ON */
	return !has_distinct_on_clause(query);
}


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

/*
 * 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) ||
		list_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 = linitial(clause->args);
	linitial(clause->args) = lsecond(clause->args);
	lsecond(clause->args) = temp;
}

/*
 * strip_implicit_coercions: remove implicit coercions at top level of tree
 *
 * Note: there isn't any useful thing we can do with a RowExpr here, so
 * just return it unchanged, even if it's marked as an implicit coercion.
 */
Node *
strip_implicit_coercions(Node *node)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, FuncExpr))
	{
		FuncExpr   *f = (FuncExpr *) node;

		if (f->funcformat == COERCE_IMPLICIT_CAST)
			return strip_implicit_coercions(linitial(f->args));
	}
	else if (IsA(node, RelabelType))
	{
		RelabelType *r = (RelabelType *) node;

		if (r->relabelformat == COERCE_IMPLICIT_CAST)
			return strip_implicit_coercions((Node *) r->arg);
	}
	else if (IsA(node, ConvertRowtypeExpr))
	{
		ConvertRowtypeExpr *c = (ConvertRowtypeExpr *) node;

		if (c->convertformat == COERCE_IMPLICIT_CAST)
			return strip_implicit_coercions((Node *) c->arg);
	}
	else if (IsA(node, CoerceToDomain))
	{
		CoerceToDomain *c = (CoerceToDomain *) node;

		if (c->coercionformat == COERCE_IMPLICIT_CAST)
			return strip_implicit_coercions((Node *) c->arg);
	}
	return node;
}

/*
 * set_coercionform_dontcare: set all CoercionForm fields to COERCE_DONTCARE
 *
 * This is used to make index expressions and index predicates more easily
 * comparable to clauses of queries.  CoercionForm is not semantically
 * significant (for cases where it does matter, the significant info is
 * coded into the coercion function arguments) so we can ignore it during
 * comparisons.  Thus, for example, an index on "foo::int4" can match an
 * implicit coercion to int4.
 *
 * Caution: the passed expression tree is modified in-place.
 */
void
set_coercionform_dontcare(Node *node)
{
	(void) set_coercionform_dontcare_walker(node, NULL);
}

static bool
set_coercionform_dontcare_walker(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, FuncExpr))
		((FuncExpr *) node)->funcformat = COERCE_DONTCARE;
	else if (IsA(node, RelabelType))
		((RelabelType *) node)->relabelformat = COERCE_DONTCARE;
	else if (IsA(node, ConvertRowtypeExpr))
		((ConvertRowtypeExpr *) node)->convertformat = COERCE_DONTCARE;
	else if (IsA(node, RowExpr))
		((RowExpr *) node)->row_format = COERCE_DONTCARE;
	else if (IsA(node, CoerceToDomain))
		((CoerceToDomain *) node)->coercionformat = COERCE_DONTCARE;
	return expression_tree_walker(node, set_coercionform_dontcare_walker,
								  context);
}

/*
 * Helper for eval_const_expressions: check that datatype of an attribute
 * is still what it was when the expression was parsed.  This is needed to
 * guard against improper simplification after ALTER COLUMN TYPE.  (XXX we
 * may well need to make similar checks elsewhere?)
 */
static bool
rowtype_field_matches(Oid rowtypeid, int fieldnum,
					  Oid expectedtype, int32 expectedtypmod)
{
	TupleDesc	tupdesc;
	Form_pg_attribute attr;

	/* No issue for RECORD, since there is no way to ALTER such a type */
	if (rowtypeid == RECORDOID)
		return true;
	tupdesc = lookup_rowtype_tupdesc(rowtypeid, -1);
	if (fieldnum <= 0 || fieldnum > tupdesc->natts)
		return false;
	attr = tupdesc->attrs[fieldnum - 1];
	if (attr->attisdropped ||
		attr->atttypid != expectedtype ||
		attr->atttypmod != expectedtypmod)
		return false;
	return true;
}


/*--------------------
 * 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.
 *
 * NOTE: the planner assumes that this will always flatten nested AND and
 * OR clauses into N-argument form.  See comments in prepqual.c.
 *--------------------
 */
Node *
eval_const_expressions(Node *node)
{
	eval_const_expressions_context context;

	context.active_fns = NIL;	/* nothing being recursively simplified */
	context.case_val = NULL;	/* no CASE being examined */
	context.estimate = false;	/* safe transformations only */
	return eval_const_expressions_mutator(node, &context);
}

/*--------------------
 * estimate_expression_value
 *
 * This function attempts to estimate the value of an expression for
 * planning purposes.  It is in essence a more aggressive version of
 * eval_const_expressions(): we will perform constant reductions that are
 * not necessarily 100% safe, but are reasonable for estimation purposes.
 *
 * Currently the extra steps that are taken in this mode are:
 * 1. Substitute values for Params, where a bound Param value has been made
 *	  available by the caller of planner().
 * 2. Fold stable, as well as immutable, functions to constants.
 *--------------------
 */
Node *
estimate_expression_value(Node *node)
{
	eval_const_expressions_context context;

	context.active_fns = NIL;	/* nothing being recursively simplified */
	context.case_val = NULL;	/* no CASE being examined */
	context.estimate = true;	/* unsafe transformations OK */
	return eval_const_expressions_mutator(node, &context);
}

static Node *
eval_const_expressions_mutator(Node *node,
							   eval_const_expressions_context *context)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, Param))
	{
		Param	   *param = (Param *) node;

		/* OK to try to substitute value? */
		if (context->estimate && param->paramkind != PARAM_EXEC &&
			PlannerBoundParamList != NULL)
		{
			ParamListInfo paramInfo;

			/* Search to see if we've been given a value for this Param */
			paramInfo = lookupParam(PlannerBoundParamList,
									param->paramkind,
									param->paramname,
									param->paramid,
									true);
			if (paramInfo)
			{
				/*
				 * Found it, so return a Const representing the param value.
				 * Note that we don't copy pass-by-ref datatypes, so the Const
				 * will only be valid as long as the bound parameter list
				 * exists. This is okay for intended uses of
				 * estimate_expression_value().
				 */
				int16		typLen;
				bool		typByVal;

				Assert(paramInfo->ptype == param->paramtype);
				get_typlenbyval(param->paramtype, &typLen, &typByVal);
				return (Node *) makeConst(param->paramtype,
										  (int) typLen,
										  paramInfo->value,
										  paramInfo->isnull,
										  typByVal);
			}
		}
		/* Not replaceable, so just copy the Param (no need to recurse) */
		return (Node *) copyObject(param);
	}
	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 *) context);

		/*
		 * 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, context);
		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 *) context);

		/*
		 * 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, context);
		if (simple)				/* successfully simplified it */
			return (Node *) simple;

		/*
		 * If the operator is boolean equality, we know how to simplify cases
		 * involving one constant and one non-constant argument.
		 */
		if (expr->opno == BooleanEqualOperator)
		{
			simple = simplify_boolean_equality(args);
			if (simple)			/* successfully simplified it */
				return (Node *) simple;
		}

		/*