postgresql/src/backend/optimizer/prep/prepqual.c

/*-------------------------------------------------------------------------
 *
 * prepqual.c
 *	  Routines for preprocessing the parse tree qualification
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.13 1999/02/13 23:16:37 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <sys/types.h>

#include "postgres.h"

#include "nodes/pg_list.h"
#include "nodes/makefuncs.h"

#include "optimizer/internal.h"
#include "optimizer/clauses.h"
#include "optimizer/prep.h"

#include "utils/lsyscache.h"

static Expr *pull_args(Expr *qual);
static List *pull_ors(List *orlist);
static List *pull_ands(List *andlist);
static Expr *find_nots(Expr *qual);
static Expr *push_nots(Expr *qual);
static Expr *normalize(Expr *qual);
static List *or_normalize(List *orlist);
static List *distribute_args(List *item, List *args);
static List *qual_cleanup(Expr *qual);
static List *remove_ands(Expr *qual);
static List *remove_duplicates(List *list);

/*****************************************************************************
 *
 *		CNF CONVERSION ROUTINES
 *
 *		NOTES:
 *		The basic algorithms for normalizing the qualification are taken
 *		from ingres/source/qrymod/norml.c
 *
 *		Remember that the initial qualification may consist of ARBITRARY
 *		combinations of clauses.  In addition, before this routine is called,
 *		the qualification will contain explicit "AND"s.
 *
 *****************************************************************************/


/*
 * cnfify
 *	  Convert a qualification to conjunctive normal form by applying
 *	  successive normalizations.
 *
 * Returns the modified qualification with an extra level of nesting.
 *
 * If 'removeAndFlag' is true then it removes the explicit ANDs.
 *
 * NOTE: this routine is called by the planner (removeAndFlag = true)
 *		and from the rule manager (removeAndFlag = false).
 *
 */
List *
cnfify(Expr *qual, bool removeAndFlag)
{
	Expr	   *newqual = NULL;

	if (qual != NULL)
	{
		newqual = find_nots(pull_args(qual));
		newqual = normalize(pull_args(newqual));
		newqual = (Expr *) qual_cleanup(pull_args(newqual));
		newqual = pull_args(newqual);;

		if (removeAndFlag)
		{
			if (and_clause((Node *) newqual))
				newqual = (Expr *) remove_ands(newqual);
			else
				newqual = (Expr *) remove_ands(make_andclause(lcons(newqual, NIL)));
		}
	}

	return (List *) (newqual);
}

/*
 * find_nots
 *	  Traverse the qualification, looking for 'not's to take care of.
 *	  For 'not' clauses, remove the 'not' and push it down to the clauses'
 *	  descendants.
 *	  For all other clause types, simply recurse.
 *
 * Returns the modified qualification.
 *
 */
static Expr *
find_nots(Expr *qual)
{
	if (qual == NULL)
		return NULL;

	if (is_opclause((Node *) qual))
	{
		return (make_clause(qual->opType, qual->oper,
							lcons(find_nots((Expr *) get_leftop(qual)),
							 lcons(find_nots((Expr *) get_rightop(qual)),
								   NIL))));
	}
	else if (and_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, find_nots(lfirst(temp)));

		return make_andclause(t_list);
	}
	else if (or_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, find_nots(lfirst(temp)));
		return make_orclause(t_list);
	}
	else if (not_clause((Node *) qual))
		return push_nots(get_notclausearg(qual));
	else
		return qual;
}

/*
 * normalize
 *	  Given a qualification tree with the 'not's pushed down, convert it
 *	  to a tree in CNF by repeatedly applying the rule:
 *				("OR" A ("AND" B C))  => ("AND" ("OR" A B) ("OR" A C))
 *	  bottom-up.
 *	  Note that 'or' clauses will always be turned into 'and' clauses.
 *
 * Returns the modified qualification.
 *
 */
static Expr *
normalize(Expr *qual)
{
	if (qual == NULL)
		return NULL;

	if (is_opclause((Node *) qual))
	{
		Expr	   *expr = (Expr *) qual;

		return (make_clause(expr->opType, expr->oper,
							lcons(normalize((Expr *) get_leftop(qual)),
							 lcons(normalize((Expr *) get_rightop(qual)),
								   NIL))));
	}
	else if (and_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, normalize(lfirst(temp)));
		return make_andclause(t_list);
	}
	else if (or_clause((Node *) qual))
	{
		/* XXX - let form, maybe incorrect */
		List	   *orlist = NIL;
		List	   *temp = NIL;
		bool		has_andclause = FALSE;

		foreach(temp, qual->args)
			orlist = lappend(orlist, normalize(lfirst(temp)));
		foreach(temp, orlist)
		{
			if (and_clause(lfirst(temp)))
			{
				has_andclause = TRUE;
				break;
			}
		}
		if (has_andclause == TRUE)
			return make_andclause(or_normalize(orlist));
		else
			return make_orclause(orlist);

	}
	else if (not_clause((Node *) qual))
		return make_notclause(normalize(get_notclausearg(qual)));
	else
		return qual;
}

/*
 * qual_cleanup
 *	  Fix up a qualification by removing duplicate entries (left over from
 *	  normalization), and by removing 'and' and 'or' clauses which have only
 *	  one valid expr (e.g., ("AND" A) => A).
 *
 * Returns the modified qualfication.
 *
 */
static List *
qual_cleanup(Expr *qual)
{
	if (qual == NULL)
		return NIL;

	if (is_opclause((Node *) qual))
	{
		return ((List *) make_clause(qual->opType, qual->oper,
							lcons(qual_cleanup((Expr *) get_leftop(qual)),
						   lcons(qual_cleanup((Expr *) get_rightop(qual)),
								 NIL))));
	}
	else if (and_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;
		List	   *new_and_args = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, qual_cleanup(lfirst(temp)));

		new_and_args = remove_duplicates(t_list);

		if (length(new_and_args) > 1)
			return (List *) make_andclause(new_and_args);
		else
			return lfirst(new_and_args);
	}
	else if (or_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;
		List	   *new_or_args = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, qual_cleanup(lfirst(temp)));

		new_or_args = remove_duplicates(t_list);


		if (length(new_or_args) > 1)
			return (List *) make_orclause(new_or_args);
		else
			return lfirst(new_or_args);
	}
	else if (not_clause((Node *) qual))
		return (List *) make_notclause((Expr *) qual_cleanup((Expr *) get_notclausearg(qual)));
	else
		return (List *) qual;
}

/*
 * pull_args
 *	  Given a qualification, eliminate nested 'and' and 'or' clauses.
 *
 * Returns the modified qualification.
 *
 */
static Expr *
pull_args(Expr *qual)
{
	if (qual == NULL)
		return NULL;

	if (is_opclause((Node *) qual))
	{
		return (make_clause(qual->opType, qual->oper,
							lcons(pull_args((Expr *) get_leftop(qual)),
							 lcons(pull_args((Expr *) get_rightop(qual)),
								   NIL))));
	}
	else if (and_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, pull_args(lfirst(temp)));
		return make_andclause(pull_ands(t_list));
	}
	else if (or_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, pull_args(lfirst(temp)));
		return make_orclause(pull_ors(t_list));
	}
	else if (not_clause((Node *) qual))
		return make_notclause(pull_args(get_notclausearg(qual)));
	else
		return qual;
}

/*
 * pull_ors
 *	  Pull the arguments of an 'or' clause nested within another 'or'
 *	  clause up into the argument list of the parent.
 *
 * Returns the modified list.
 */
static List *
pull_ors(List *orlist)
{
	if (orlist == NIL)
		return NIL;

	if (or_clause(lfirst(orlist)))
	{
		List	   *args = ((Expr *) lfirst(orlist))->args;

		return (pull_ors(nconc(copyObject((Node *) args),
							   copyObject((Node *) lnext(orlist)))));
	}
	else
		return lcons(lfirst(orlist), pull_ors(lnext(orlist)));
}

/*
 * pull_ands
 *	  Pull the arguments of an 'and' clause nested within another 'and'
 *	  clause up into the argument list of the parent.
 *
 * Returns the modified list.
 */
static List *
pull_ands(List *andlist)
{
	if (andlist == NIL)
		return NIL;

	if (and_clause(lfirst(andlist)))
	{
		List	   *args = ((Expr *) lfirst(andlist))->args;

		return (pull_ands(nconc(copyObject((Node *) args),
								copyObject((Node *) lnext(andlist)))));
	}
	else
		return lcons(lfirst(andlist), pull_ands(lnext(andlist)));
}

/*
 * push_nots
 *	  Negate the descendants of a 'not' clause.
 *
 * Returns the modified qualification.
 *
 */
static Expr *
push_nots(Expr *qual)
{
	if (qual == NULL)
		return NULL;

	/*
	 * Negate an operator clause if possible: ("NOT" (< A B)) => (> A B)
	 * Otherwise, retain the clause as it is (the 'not' can't be pushed
	 * down any farther).
	 */
	if (is_opclause((Node *) qual))
	{
		Oper	   *oper = (Oper *) ((Expr *) qual)->oper;
		Oid			negator = get_negator(oper->opno);

		if (negator)
		{
			Oper	   *op = (Oper *) makeOper(negator,
											   InvalidOid,
											   oper->opresulttype,
											   0, NULL);

			op->op_fcache = (FunctionCache *) NULL;
			return (make_opclause(op, get_leftop(qual), get_rightop(qual)));
		}
		else
			return make_notclause(qual);
	}
	else if (and_clause((Node *) qual))
	{

		/*
		 * Apply DeMorgan's Laws: ("NOT" ("AND" A B)) => ("OR" ("NOT" A)
		 * ("NOT" B)) ("NOT" ("OR" A B)) => ("AND" ("NOT" A) ("NOT" B))
		 * i.e., continue negating down through the clause's descendants.
		 */
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, push_nots(lfirst(temp)));
		return make_orclause(t_list);
	}
	else if (or_clause((Node *) qual))
	{
		List	   *temp = NIL;
		List	   *t_list = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, push_nots(lfirst(temp)));
		return make_andclause(t_list);
	}
	else if (not_clause((Node *) qual))

		/*
		 * Another 'not' cancels this 'not', so eliminate the 'not' and
		 * stop negating this branch.
		 */
		return find_nots(get_notclausearg(qual));
	else

		/*
		 * We don't know how to negate anything else, place a 'not' at
		 * this level.
		 */
		return make_notclause(qual);
}

/*
 * or_normalize
 *	  Given a list of exprs which are 'or'ed together, distribute any
 *	  'and' clauses.
 *
 * Returns the modified list.
 *
 */
static List *
or_normalize(List *orlist)
{
	List	   *distributable = NIL;
	List	   *new_orlist = NIL;
	List	   *temp = NIL;

	if (orlist == NIL)
		return NIL;

	foreach(temp, orlist)
	{
		if (and_clause(lfirst(temp)))
			distributable = lfirst(temp);
	}
	if (distributable)
		new_orlist = LispRemove(distributable, orlist);

	if (new_orlist)
	{
		return (or_normalize(lcons(distribute_args(lfirst(new_orlist),
										 ((Expr *) distributable)->args),
								lnext(new_orlist))));
	}
	else
		return orlist;
}

/*
 * distribute_args
 *	  Create new 'or' clauses by or'ing 'item' with each element of 'args'.
 *	  E.g.: (distribute-args A ("AND" B C)) => ("AND" ("OR" A B) ("OR" A C))
 *
 * Returns an 'and' clause.
 *
 */
static List *
distribute_args(List *item, List *args)
{
	List	   *or_list = NIL;
	List	   *n_list = NIL;
	List	   *temp = NIL;
	List	   *t_list = NIL;

	if (args == NULL)
		return item;

	foreach(temp, args)
	{
		n_list = or_normalize(pull_ors(lcons(item,
											 lcons(lfirst(temp), NIL))));
		or_list = (List *) make_orclause(n_list);
		t_list = lappend(t_list, or_list);
	}
	return (List *) make_andclause(t_list);
}

/*
 * remove_ands
 *	  Remove the explicit "AND"s from the qualification:
 *				("AND" A B) => (A B)
 *
 * RETURNS : qual
 * MODIFIES: qual
 */
static List *
remove_ands(Expr *qual)
{
	List	   *t_list = NIL;

	if (qual == NULL)
		return NIL;
	if (is_opclause((Node *) qual))
	{
		return ((List *) make_clause(qual->opType, qual->oper,
							lcons(remove_ands((Expr *) get_leftop(qual)),
						   lcons(remove_ands((Expr *) get_rightop(qual)),
								 NIL))));
	}
	else if (and_clause((Node *) qual))
	{
		List	   *temp = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, remove_ands(lfirst(temp)));
		return t_list;
	}
	else if (or_clause((Node *) qual))
	{
		List	   *temp = NIL;

		foreach(temp, qual->args)
			t_list = lappend(t_list, remove_ands(lfirst(temp)));
		return (List *) make_orclause((List *) t_list);
	}
	else if (not_clause((Node *) qual))
		return (List *) make_notclause((Expr *) remove_ands((Expr *) get_notclausearg(qual)));
	else
		return (List *) qual;
}

/*
 * remove_duplicates
 */
static List *
remove_duplicates(List *list)
{
	List	   *i;
	List	   *j;
	List	   *result = NIL;
	bool		there_exists_duplicate = false;

	if (length(list) == 1)
		return list;

	foreach(i, list)
	{
		if (i != NIL)
		{
			foreach(j, lnext(i))
			{
				if (equal(lfirst(i), lfirst(j)))
					there_exists_duplicate = true;
			}
			if (!there_exists_duplicate)
				result = lappend(result, lfirst(i));

			there_exists_duplicate = false;
		}
	}
	return result;
}