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 1.3 1997/08/20 14:53:30 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 *qualcleanup(Expr *qual);
static List *remove_ands(Expr *qual);
static List *remove_duplicates(List *list);

/*    
 * preprocess-qualification--
 *    Driver routine for modifying the parse tree qualification.
 *    
 * Returns the new base qualification and the existential qualification
 * in existentialQualPtr.
 *    
 *  XXX right now, update_clauses() does nothing so 
 *      preprocess-qualification simply converts the qual in conjunctive
 *      normal form  (see cnfify() below ) 
 */
List *
preprocess_qualification(Expr *qual, List *tlist, List **existentialQualPtr)
{
    List *cnf_qual = cnfify(qual, true);
/*
    List *existential_qual =
	update_clauses(intCons(_query_result_relation_,
				update_relations(tlist)),
		       cnf_qual,
		       _query_command_type_);
    if (existential_qual) {
	*existentialQualPtr = existential_qual;
	return set_difference(cnf_qual, existential_qual);
    } else {
	*existentialQualPtr = NIL;
	return cnf_qual;
    }
*/
 /* update_clauses() is not working right now */
    *existentialQualPtr = NIL;
    return cnf_qual;

}

/*****************************************************************************
 *
 *     	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*)qualcleanup(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)));
	}
    }
    else if (qual!=NULL)
	newqual = (Expr*)lcons(qual, NIL);

    return (List*)(newqual);
}

/*    
 * 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))));
    }
}

/*    
 * 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);
}

/*    
 * 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));
}

/*    
 * 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);
}

/*    
 * 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));
}

/*    
 * qualcleanup--
 *    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 *
qualcleanup(Expr *qual)
{
    if (qual==NULL) 
	return (NIL);
    
    if (is_opclause((Node*)qual)) {
	return ((List*)make_clause(qual->opType, qual->oper,
				   lcons(qualcleanup((Expr*)get_leftop(qual)),
					lcons(qualcleanup((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,qualcleanup(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,qualcleanup(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*)qualcleanup((Expr*)get_notclausearg(qual))));
				
    else 
	return ((List*)qual);
}

/*    
 * 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);
    }
}

/*****************************************************************************
 *
 *     	EXISTENTIAL QUALIFICATIONS
 *
 *****************************************************************************/

/*    
 * update-relations--
 *    Returns the range table indices (i.e., varnos) for all relations which
 *    are referenced in the target list.
 *    
 */
#ifdef NOT_USED 
static List *
update_relations(List *tlist)
{
    return(NIL);
}
#endif

/*****************************************************************************
 *
 *
 *
 *****************************************************************************/

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);
}