Further improvements in cnfify: reduce amount of self-recursion
in or_normalize, remove detection of duplicate subexpressions (since it's highly unlikely to be worth the amount of time it takes), and introduce a dnfify() entry point so that unintelligible backwards logic in UNION processing can be eliminated. This is just an intermediate step --- next thing is to look at not forcing the qual into CNF form when it would be better off in DNF form.
This commit is contained in:
Tom Lane
parent
4644fc8071
commit
2119cc0670
@ -1,13 +1,13 @@
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/*-------------------------------------------------------------------------
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*
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* prepqual.c
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* Routines for preprocessing the parse tree qualification
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* Routines for preprocessing qualification expressions
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*
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* Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.18 1999/09/07 03:47:06 tgl Exp $
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* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.19 1999/09/12 18:08:17 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -20,28 +20,33 @@
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#include "optimizer/prep.h"
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#include "utils/lsyscache.h"
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static Expr *flatten_andors(Expr *qual, bool deep);
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static Expr *flatten_andors(Expr *qual);
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static List *pull_ors(List *orlist);
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static List *pull_ands(List *andlist);
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static Expr *find_nots(Expr *qual);
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static Expr *push_nots(Expr *qual);
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static Expr *normalize(Expr *qual);
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static List *or_normalize(List *orlist);
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static List *distribute_args(List *item, List *args);
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static List *qual_cleanup(Expr *qual);
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static List *remove_duplicates(List *list);
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static Expr *find_ors(Expr *qual);
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static Expr *or_normalize(List *orlist);
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static Expr *find_ands(Expr *qual);
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static Expr *and_normalize(List *andlist);
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/*****************************************************************************
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*
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* CNF CONVERSION ROUTINES
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* CNF/DNF CONVERSION ROUTINES
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*
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* NOTES:
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* The basic algorithms for normalizing the qualification are taken
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* from ingres/source/qrymod/norml.c
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* These routines convert an arbitrary boolean expression into
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* conjunctive normal form or disjunctive normal form.
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*
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* Remember that the initial qualification may consist of ARBITRARY
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* combinations of clauses. In addition, before this routine is called,
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* the qualification will contain explicit "AND"s.
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* The result of these routines differs from a "true" CNF/DNF in that
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* we do not bother to detect common subexpressions; e.g., ("AND" A A)
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* does not get simplified to A. Testing for identical subexpressions
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* is a waste of time if the query is written intelligently, and it
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* takes an unreasonable amount of time if there are many subexpressions
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* (since it's roughly O(N^2) in the number of subexpressions).
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*
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* Because of that restriction, it would be unwise to apply dnfify()
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* to the result of cnfify() or vice versa. Instead apply both to
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* the original user-written qual expression.
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*
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*****************************************************************************/
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@ -54,308 +59,70 @@ static List *remove_duplicates(List *list);
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* Returns the modified qualification.
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*
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* If 'removeAndFlag' is true then it removes explicit AND at the top level,
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* producing a list of implicitly-ANDed conditions. Otherwise, a normal
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* boolean expression is returned.
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*
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* NOTE: this routine is called by the planner (removeAndFlag = true)
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* and from the rule manager (removeAndFlag = false).
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*
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* producing a list of implicitly-ANDed conditions. Otherwise, a regular
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* boolean expression is returned. Since most callers pass 'true', we
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* prefer to declare the result as List *, not Expr *.
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*/
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List *
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cnfify(Expr *qual, bool removeAndFlag)
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{
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Expr *newqual = NULL;
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Expr *newqual;
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if (qual != NULL)
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{
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/* Flatten AND and OR groups throughout the tree.
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* This improvement is always worthwhile.
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*/
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newqual = flatten_andors(qual, true);
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/* Push down NOTs. We do this only in the top-level boolean
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* expression, without examining arguments of operators/functions.
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*/
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newqual = find_nots(newqual);
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/* Pushing NOTs could have brought AND/ORs together, so do
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* another flatten_andors (only in the top level); then normalize.
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*/
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newqual = normalize(flatten_andors(newqual, false));
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/* Do we need a flatten here? Anyway, clean up after normalize. */
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newqual = (Expr *) qual_cleanup(flatten_andors(newqual, false));
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/* This flatten is almost surely a waste of time... */
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newqual = flatten_andors(newqual, false);
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if (removeAndFlag)
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{
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newqual = (Expr *) make_ands_implicit(newqual);
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}
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}
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return (List *) (newqual);
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}
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/*
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* find_nots
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* Traverse the qualification, looking for 'NOT's to take care of.
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* For 'NOT' clauses, apply push_not() to try to push down the 'NOT'.
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* For all other clause types, simply recurse.
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*
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* Returns the modified qualification.
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*
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*/
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static Expr *
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find_nots(Expr *qual)
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{
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if (qual == NULL)
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return NULL;
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#ifdef NOT_USED
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/* recursing into operator expressions is probably not worth it. */
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if (is_opclause((Node *) qual))
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{
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Expr *left = (Expr *) get_leftop(qual);
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Expr *right = (Expr *) get_rightop(qual);
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if (right)
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return make_clause(qual->opType, qual->oper,
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lcons(find_nots(left),
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lcons(find_nots(right),
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NIL)));
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else
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return make_clause(qual->opType, qual->oper,
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lcons(find_nots(left),
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NIL));
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}
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#endif
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if (and_clause((Node *) qual))
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{
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List *t_list = NIL;
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List *temp;
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foreach(temp, qual->args)
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t_list = lappend(t_list, find_nots(lfirst(temp)));
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return make_andclause(t_list);
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}
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else if (or_clause((Node *) qual))
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{
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List *t_list = NIL;
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List *temp;
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foreach(temp, qual->args)
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t_list = lappend(t_list, find_nots(lfirst(temp)));
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return make_orclause(t_list);
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}
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else if (not_clause((Node *) qual))
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return push_nots(get_notclausearg(qual));
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else
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return qual;
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}
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/*
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* push_nots
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* Push down a 'NOT' as far as possible.
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*
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* Input is an expression to be negated (e.g., the argument of a NOT clause).
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* Returns a new qual equivalent to the negation of the given qual.
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*/
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static Expr *
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push_nots(Expr *qual)
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{
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if (qual == NULL)
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return make_notclause(qual); /* XXX is this right? Or possible? */
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/*
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* Negate an operator clause if possible: ("NOT" (< A B)) => (> A B)
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* Otherwise, retain the clause as it is (the 'not' can't be pushed
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* down any farther).
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*/
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if (is_opclause((Node *) qual))
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{
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Oper *oper = (Oper *) ((Expr *) qual)->oper;
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Oid negator = get_negator(oper->opno);
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if (negator)
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{
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Oper *op = (Oper *) makeOper(negator,
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InvalidOid,
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oper->opresulttype,
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0, NULL);
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return make_opclause(op, get_leftop(qual), get_rightop(qual));
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}
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else
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return make_notclause(qual);
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}
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else if (and_clause((Node *) qual))
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{
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/*
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* Apply DeMorgan's Laws: ("NOT" ("AND" A B)) => ("OR" ("NOT" A)
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* ("NOT" B)) ("NOT" ("OR" A B)) => ("AND" ("NOT" A) ("NOT" B))
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* i.e., continue negating down through the clause's descendants.
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*/
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List *t_list = NIL;
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List *temp;
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foreach(temp, qual->args)
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t_list = lappend(t_list, push_nots(lfirst(temp)));
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return make_orclause(t_list);
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}
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else if (or_clause((Node *) qual))
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{
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List *t_list = NIL;
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List *temp;
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foreach(temp, qual->args)
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t_list = lappend(t_list, push_nots(lfirst(temp)));
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return make_andclause(t_list);
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}
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else if (not_clause((Node *) qual))
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{
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/*
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* Another 'not' cancels this 'not', so eliminate the 'not' and
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* stop negating this branch. But search the subexpression for
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* more 'not's to simplify.
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*/
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return find_nots(get_notclausearg(qual));
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}
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else
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{
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/*
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* We don't know how to negate anything else, place a 'not' at
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* this level.
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*/
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return make_notclause(qual);
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}
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}
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/*
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* normalize
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* Given a qualification tree with the 'not's pushed down, convert it
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* to a tree in CNF by repeatedly applying the rule:
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* ("OR" A ("AND" B C)) => ("AND" ("OR" A B) ("OR" A C))
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* bottom-up.
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* Note that 'or' clauses will always be turned into 'and' clauses
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* if they contain any 'and' subclauses. XXX this is not always
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* an improvement...
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*
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* Returns the modified qualification.
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*
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*/
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static Expr *
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normalize(Expr *qual)
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{
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if (qual == NULL)
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return NULL;
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/* We used to recurse into opclauses here, but I see no reason to... */
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if (and_clause((Node *) qual))
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{
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List *t_list = NIL;
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List *temp;
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foreach(temp, qual->args)
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t_list = lappend(t_list, normalize(lfirst(temp)));
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return make_andclause(t_list);
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}
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else if (or_clause((Node *) qual))
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{
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/* XXX - let form, maybe incorrect */
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List *orlist = NIL;
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bool has_andclause = false;
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List *temp;
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foreach(temp, qual->args)
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orlist = lappend(orlist, normalize(lfirst(temp)));
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foreach(temp, orlist)
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{
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if (and_clause(lfirst(temp)))
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{
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has_andclause = true;
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break;
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}
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}
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if (has_andclause)
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return make_andclause(or_normalize(orlist));
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else
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return make_orclause(orlist);
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}
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else if (not_clause((Node *) qual))
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return make_notclause(normalize(get_notclausearg(qual)));
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else
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return qual;
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}
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/*
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* qual_cleanup
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* Fix up a qualification by removing duplicate entries (left over from
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* normalization), and by removing 'and' and 'or' clauses which have only
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* one remaining subexpr (e.g., ("AND" A) => A).
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*
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* Returns the modified qualification.
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*/
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static List *
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qual_cleanup(Expr *qual)
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{
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if (qual == NULL)
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return NIL;
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if (is_opclause((Node *) qual))
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/* Flatten AND and OR groups throughout the tree.
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* This improvement is always worthwhile.
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*/
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newqual = flatten_andors(qual);
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/* Push down NOTs. We do this only in the top-level boolean
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* expression, without examining arguments of operators/functions.
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*/
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newqual = find_nots(newqual);
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/* Normalize into conjunctive normal form. */
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newqual = find_ors(newqual);
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if (removeAndFlag)
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{
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Expr *left = (Expr *) get_leftop(qual);
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Expr *right = (Expr *) get_rightop(qual);
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if (right)
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return (List *) make_clause(qual->opType, qual->oper,
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lcons(qual_cleanup(left),
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lcons(qual_cleanup(right),
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NIL)));
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else
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return (List *) make_clause(qual->opType, qual->oper,
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lcons(qual_cleanup(left),
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NIL));
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newqual = (Expr *) make_ands_implicit(newqual);
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}
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else if (and_clause((Node *) qual))
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{
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List *t_list = NIL;
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List *temp;
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List *new_and_args;
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foreach(temp, qual->args)
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t_list = lappend(t_list, qual_cleanup(lfirst(temp)));
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return (List *) newqual;
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}
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new_and_args = remove_duplicates(t_list);
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/*
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* dnfify
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* Convert a qualification to disjunctive normal form by applying
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* successive normalizations.
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*
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* Returns the modified qualification.
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*
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* We do not offer a 'removeOrFlag' in this case; the usages are
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* different.
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*/
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Expr *
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dnfify(Expr *qual)
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{
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Expr *newqual;
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if (length(new_and_args) > 1)
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return (List *) make_andclause(new_and_args);
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else
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return lfirst(new_and_args);
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}
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else if (or_clause((Node *) qual))
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{
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List *t_list = NIL;
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List *temp;
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List *new_or_args;
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if (qual == NULL)
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return NULL;
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foreach(temp, qual->args)
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t_list = lappend(t_list, qual_cleanup(lfirst(temp)));
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/* Flatten AND and OR groups throughout the tree.
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* This improvement is always worthwhile.
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*/
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newqual = flatten_andors(qual);
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/* Push down NOTs. We do this only in the top-level boolean
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* expression, without examining arguments of operators/functions.
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*/
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newqual = find_nots(newqual);
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/* Normalize into disjunctive normal form. */
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newqual = find_ands(newqual);
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new_or_args = remove_duplicates(t_list);
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if (length(new_or_args) > 1)
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return (List *) make_orclause(new_or_args);
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else
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return lfirst(new_or_args);
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}
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else if (not_clause((Node *) qual))
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return (List *) make_notclause((Expr *) qual_cleanup((Expr *) get_notclausearg(qual)));
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else
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return (List *) qual;
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return newqual;
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}
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/*--------------------
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* flatten_andors
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* Given a qualification, simplify nested AND/OR clauses into flat
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* AND/OR clauses with more arguments.
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*
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* The parser regards AND and OR as purely binary operators, so a qual like
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* (A = 1) OR (A = 2) OR (A = 3) ...
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* will produce a nested parsetree
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@ -363,16 +130,24 @@ qual_cleanup(Expr *qual)
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* In reality, the optimizer and executor regard AND and OR as n-argument
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* operators, so this tree can be flattened to
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* (OR (A = 1) (A = 2) (A = 3) ...)
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* which is the responsibility of this routine.
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* which is the responsibility of the routines below.
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*
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* If 'deep' is true, we search the whole tree for AND/ORs to simplify;
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* if not, we consider only the top-level AND/OR/NOT structure.
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* flatten_andors() does the basic transformation with no initial assumptions.
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* pull_ands() and pull_ors() are used to maintain flatness of the AND/OR
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* tree after local transformations that might introduce nested AND/ORs.
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*--------------------
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*/
|
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/*--------------------
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* flatten_andors
|
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* Given a qualification, simplify nested AND/OR clauses into flat
|
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* AND/OR clauses with more arguments.
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*
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* Returns the rebuilt expr (note original list structure is not touched).
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*--------------------
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*/
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static Expr *
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flatten_andors(Expr *qual, bool deep)
|
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flatten_andors(Expr *qual)
|
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{
|
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if (qual == NULL)
|
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return NULL;
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@ -384,7 +159,7 @@ flatten_andors(Expr *qual, bool deep)
|
||||
|
||||
foreach(arg, qual->args)
|
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{
|
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Expr *subexpr = flatten_andors((Expr *) lfirst(arg), deep);
|
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Expr *subexpr = flatten_andors((Expr *) lfirst(arg));
|
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|
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/*
|
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* Note: we can destructively nconc the subexpression's arglist
|
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@ -406,7 +181,7 @@ flatten_andors(Expr *qual, bool deep)
|
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|
||||
foreach(arg, qual->args)
|
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{
|
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Expr *subexpr = flatten_andors((Expr *) lfirst(arg), deep);
|
||||
Expr *subexpr = flatten_andors((Expr *) lfirst(arg));
|
||||
|
||||
/*
|
||||
* Note: we can destructively nconc the subexpression's arglist
|
||||
@ -422,20 +197,20 @@ flatten_andors(Expr *qual, bool deep)
|
||||
return make_orclause(out_list);
|
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}
|
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else if (not_clause((Node *) qual))
|
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return make_notclause(flatten_andors(get_notclausearg(qual), deep));
|
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else if (deep && is_opclause((Node *) qual))
|
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return make_notclause(flatten_andors(get_notclausearg(qual)));
|
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else if (is_opclause((Node *) qual))
|
||||
{
|
||||
Expr *left = (Expr *) get_leftop(qual);
|
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Expr *right = (Expr *) get_rightop(qual);
|
||||
|
||||
if (right)
|
||||
return make_clause(qual->opType, qual->oper,
|
||||
lcons(flatten_andors(left, deep),
|
||||
lcons(flatten_andors(right, deep),
|
||||
lcons(flatten_andors(left),
|
||||
lcons(flatten_andors(right),
|
||||
NIL)));
|
||||
else
|
||||
return make_clause(qual->opType, qual->oper,
|
||||
lcons(flatten_andors(left, deep),
|
||||
lcons(flatten_andors(left),
|
||||
NIL));
|
||||
}
|
||||
else
|
||||
@ -506,89 +281,363 @@ pull_ands(List *andlist)
|
||||
}
|
||||
|
||||
/*
|
||||
* or_normalize
|
||||
* Given a list of exprs which are 'or'ed together, distribute any
|
||||
* 'and' clauses.
|
||||
*
|
||||
* Returns the modified list.
|
||||
* find_nots
|
||||
* Traverse the qualification, looking for 'NOT's to take care of.
|
||||
* For 'NOT' clauses, apply push_not() to try to push down the 'NOT'.
|
||||
* For all other clause types, simply recurse.
|
||||
*
|
||||
* Returns the modified qualification. AND/OR flatness is preserved.
|
||||
*/
|
||||
static List *
|
||||
or_normalize(List *orlist)
|
||||
static Expr *
|
||||
find_nots(Expr *qual)
|
||||
{
|
||||
List *distributable = NIL;
|
||||
List *new_orlist = NIL;
|
||||
List *temp = NIL;
|
||||
if (qual == NULL)
|
||||
return NULL;
|
||||
|
||||
if (orlist == NIL)
|
||||
return NIL;
|
||||
|
||||
foreach(temp, orlist)
|
||||
#ifdef NOT_USED
|
||||
/* recursing into operator expressions is probably not worth it. */
|
||||
if (is_opclause((Node *) qual))
|
||||
{
|
||||
if (and_clause(lfirst(temp)))
|
||||
{
|
||||
distributable = lfirst(temp);
|
||||
break;
|
||||
}
|
||||
Expr *left = (Expr *) get_leftop(qual);
|
||||
Expr *right = (Expr *) get_rightop(qual);
|
||||
|
||||
if (right)
|
||||
return make_clause(qual->opType, qual->oper,
|
||||
lcons(find_nots(left),
|
||||
lcons(find_nots(right),
|
||||
NIL)));
|
||||
else
|
||||
return make_clause(qual->opType, qual->oper,
|
||||
lcons(find_nots(left),
|
||||
NIL));
|
||||
}
|
||||
if (distributable)
|
||||
new_orlist = LispRemove(distributable, orlist);
|
||||
|
||||
if (new_orlist)
|
||||
#endif
|
||||
if (and_clause((Node *) qual))
|
||||
{
|
||||
return or_normalize(lcons(distribute_args(lfirst(new_orlist),
|
||||
((Expr *) distributable)->args),
|
||||
lnext(new_orlist)));
|
||||
List *t_list = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
t_list = lappend(t_list, find_nots(lfirst(temp)));
|
||||
return make_andclause(pull_ands(t_list));
|
||||
}
|
||||
else if (or_clause((Node *) qual))
|
||||
{
|
||||
List *t_list = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
t_list = lappend(t_list, find_nots(lfirst(temp)));
|
||||
return make_orclause(pull_ors(t_list));
|
||||
}
|
||||
else if (not_clause((Node *) qual))
|
||||
return push_nots(get_notclausearg(qual));
|
||||
else
|
||||
return qual;
|
||||
}
|
||||
|
||||
/*
|
||||
* push_nots
|
||||
* Push down a 'NOT' as far as possible.
|
||||
*
|
||||
* Input is an expression to be negated (e.g., the argument of a NOT clause).
|
||||
* Returns a new qual equivalent to the negation of the given qual.
|
||||
*/
|
||||
static Expr *
|
||||
push_nots(Expr *qual)
|
||||
{
|
||||
if (qual == NULL)
|
||||
return make_notclause(qual); /* XXX is this right? Or possible? */
|
||||
|
||||
/*
|
||||
* 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);
|
||||
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., swap AND for OR and negate all the subclauses.
|
||||
*--------------------
|
||||
*/
|
||||
List *t_list = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
t_list = lappend(t_list, push_nots(lfirst(temp)));
|
||||
return make_orclause(pull_ors(t_list));
|
||||
}
|
||||
else if (or_clause((Node *) qual))
|
||||
{
|
||||
List *t_list = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
t_list = lappend(t_list, push_nots(lfirst(temp)));
|
||||
return make_andclause(pull_ands(t_list));
|
||||
}
|
||||
else if (not_clause((Node *) qual))
|
||||
{
|
||||
/*
|
||||
* Another 'not' cancels this 'not', so eliminate the 'not' and
|
||||
* stop negating this branch. But search the subexpression for
|
||||
* more 'not's to simplify.
|
||||
*/
|
||||
return find_nots(get_notclausearg(qual));
|
||||
}
|
||||
else
|
||||
return orlist;
|
||||
{
|
||||
/*
|
||||
* We don't know how to negate anything else, place a 'not' at
|
||||
* this level.
|
||||
*/
|
||||
return make_notclause(qual);
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* 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))
|
||||
* find_ors
|
||||
* 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))
|
||||
*
|
||||
* Returns an 'and' clause.
|
||||
* Note that 'or' clauses will always be turned into 'and' clauses
|
||||
* if they contain any 'and' subclauses.
|
||||
*
|
||||
* Returns the modified qualification. AND/OR flatness is preserved.
|
||||
*/
|
||||
static List *
|
||||
distribute_args(List *item, List *args)
|
||||
static Expr *
|
||||
find_ors(Expr *qual)
|
||||
{
|
||||
List *t_list = NIL;
|
||||
if (qual == NULL)
|
||||
return NULL;
|
||||
|
||||
/* We used to recurse into opclauses here, but I see no reason to... */
|
||||
if (and_clause((Node *) qual))
|
||||
{
|
||||
List *andlist = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
andlist = lappend(andlist, find_ors(lfirst(temp)));
|
||||
return make_andclause(pull_ands(andlist));
|
||||
}
|
||||
else if (or_clause((Node *) qual))
|
||||
{
|
||||
List *orlist = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
orlist = lappend(orlist, find_ors(lfirst(temp)));
|
||||
return or_normalize(pull_ors(orlist));
|
||||
}
|
||||
else if (not_clause((Node *) qual))
|
||||
return make_notclause(find_ors(get_notclausearg(qual)));
|
||||
else
|
||||
return qual;
|
||||
}
|
||||
|
||||
/*
|
||||
* or_normalize
|
||||
* Given a list of exprs which are 'or'ed together, try to apply
|
||||
* the distributive law
|
||||
* ("OR" A ("AND" B C)) => ("AND" ("OR" A B) ("OR" A C))
|
||||
* to convert the top-level OR clause to a top-level AND clause.
|
||||
*
|
||||
* Returns the resulting expression (could be an AND clause, an OR
|
||||
* clause, or maybe even a single subexpression).
|
||||
*/
|
||||
static Expr *
|
||||
or_normalize(List *orlist)
|
||||
{
|
||||
Expr *distributable = NULL;
|
||||
int num_subclauses = 1;
|
||||
List *andclauses = NIL;
|
||||
List *temp;
|
||||
|
||||
if (args == NULL)
|
||||
return item;
|
||||
if (orlist == NIL)
|
||||
return NULL; /* probably can't happen */
|
||||
if (lnext(orlist) == NIL)
|
||||
return lfirst(orlist); /* single-expression OR (can this happen?) */
|
||||
|
||||
foreach(temp, args)
|
||||
/*
|
||||
* If we have a choice of AND clauses, pick the one with the
|
||||
* most subclauses. Because we initialized num_subclauses = 1,
|
||||
* any AND clauses with only one arg will be ignored as useless.
|
||||
*/
|
||||
foreach(temp, orlist)
|
||||
{
|
||||
List *n_list;
|
||||
Expr *clause = lfirst(temp);
|
||||
|
||||
n_list = or_normalize(pull_ors(lcons(item,
|
||||
lcons(lfirst(temp),
|
||||
NIL))));
|
||||
t_list = lappend(t_list, make_orclause(n_list));
|
||||
if (and_clause((Node *) clause))
|
||||
{
|
||||
int nclauses = length(clause->args);
|
||||
|
||||
if (nclauses > num_subclauses)
|
||||
{
|
||||
distributable = clause;
|
||||
num_subclauses = nclauses;
|
||||
}
|
||||
}
|
||||
}
|
||||
return (List *) make_andclause(t_list);
|
||||
|
||||
/* if there's no suitable AND clause, we can't transform the OR */
|
||||
if (! distributable)
|
||||
return make_orclause(orlist);
|
||||
|
||||
/* Caution: lremove destructively modifies the input orlist.
|
||||
* This should be OK, since or_normalize is only called with
|
||||
* freshly constructed lists that are not referenced elsewhere.
|
||||
*/
|
||||
orlist = lremove(distributable, orlist);
|
||||
|
||||
foreach(temp, distributable->args)
|
||||
{
|
||||
Expr *andclause = lfirst(temp);
|
||||
|
||||
/* pull_ors is needed here in case andclause has a top-level OR.
|
||||
* Then we recursively apply or_normalize, since there might
|
||||
* be an AND subclause in the resulting OR-list.
|
||||
* Note: we rely on pull_ors to build a fresh list,
|
||||
* and not damage the given orlist.
|
||||
*/
|
||||
andclause = or_normalize(pull_ors(lcons(andclause, orlist)));
|
||||
andclauses = lappend(andclauses, andclause);
|
||||
}
|
||||
|
||||
/* pull_ands is needed in case any sub-or_normalize succeeded */
|
||||
return make_andclause(pull_ands(andclauses));
|
||||
}
|
||||
|
||||
/*
|
||||
* remove_duplicates
|
||||
* find_ands
|
||||
* Given a qualification tree with the 'not's pushed down, convert it
|
||||
* to a tree in DNF by repeatedly applying the rule:
|
||||
* ("AND" A ("OR" B C)) => ("OR" ("AND" A B) ("AND" A C))
|
||||
*
|
||||
* Note that 'and' clauses will always be turned into 'or' clauses
|
||||
* if they contain any 'or' subclauses.
|
||||
*
|
||||
* Returns the modified qualification. AND/OR flatness is preserved.
|
||||
*/
|
||||
static List *
|
||||
remove_duplicates(List *list)
|
||||
static Expr *
|
||||
find_ands(Expr *qual)
|
||||
{
|
||||
List *result = NIL;
|
||||
List *i;
|
||||
if (qual == NULL)
|
||||
return NULL;
|
||||
|
||||
if (length(list) == 1)
|
||||
return list;
|
||||
|
||||
foreach(i, list)
|
||||
/* We used to recurse into opclauses here, but I see no reason to... */
|
||||
if (or_clause((Node *) qual))
|
||||
{
|
||||
if (! member(lfirst(i), result))
|
||||
result = lappend(result, lfirst(i));
|
||||
List *orlist = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
orlist = lappend(orlist, find_ands(lfirst(temp)));
|
||||
return make_orclause(pull_ors(orlist));
|
||||
}
|
||||
return result;
|
||||
else if (and_clause((Node *) qual))
|
||||
{
|
||||
List *andlist = NIL;
|
||||
List *temp;
|
||||
|
||||
foreach(temp, qual->args)
|
||||
andlist = lappend(andlist, find_ands(lfirst(temp)));
|
||||
return and_normalize(pull_ands(andlist));
|
||||
}
|
||||
else if (not_clause((Node *) qual))
|
||||
return make_notclause(find_ands(get_notclausearg(qual)));
|
||||
else
|
||||
return qual;
|
||||
}
|
||||
|
||||
/*
|
||||
* and_normalize
|
||||
* Given a list of exprs which are 'and'ed together, try to apply
|
||||
* the distributive law
|
||||
* ("AND" A ("OR" B C)) => ("OR" ("AND" A B) ("AND" A C))
|
||||
* to convert the top-level AND clause to a top-level OR clause.
|
||||
*
|
||||
* Returns the resulting expression (could be an AND clause, an OR
|
||||
* clause, or maybe even a single subexpression).
|
||||
*/
|
||||
static Expr *
|
||||
and_normalize(List *andlist)
|
||||
{
|
||||
Expr *distributable = NULL;
|
||||
int num_subclauses = 1;
|
||||
List *orclauses = NIL;
|
||||
List *temp;
|
||||
|
||||
if (andlist == NIL)
|
||||
return NULL; /* probably can't happen */
|
||||
if (lnext(andlist) == NIL)
|
||||
return lfirst(andlist); /* single-expression AND (can this happen?) */
|
||||
|
||||
/*
|
||||
* If we have a choice of OR clauses, pick the one with the
|
||||
* most subclauses. Because we initialized num_subclauses = 1,
|
||||
* any OR clauses with only one arg will be ignored as useless.
|
||||
*/
|
||||
foreach(temp, andlist)
|
||||
{
|
||||
Expr *clause = lfirst(temp);
|
||||
|
||||
if (or_clause((Node *) clause))
|
||||
{
|
||||
int nclauses = length(clause->args);
|
||||
|
||||
if (nclauses > num_subclauses)
|
||||
{
|
||||
distributable = clause;
|
||||
num_subclauses = nclauses;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/* if there's no suitable OR clause, we can't transform the AND */
|
||||
if (! distributable)
|
||||
return make_andclause(andlist);
|
||||
|
||||
/* Caution: lremove destructively modifies the input andlist.
|
||||
* This should be OK, since and_normalize is only called with
|
||||
* freshly constructed lists that are not referenced elsewhere.
|
||||
*/
|
||||
andlist = lremove(distributable, andlist);
|
||||
|
||||
foreach(temp, distributable->args)
|
||||
{
|
||||
Expr *orclause = lfirst(temp);
|
||||
|
||||
/* pull_ands is needed here in case orclause has a top-level AND.
|
||||
* Then we recursively apply and_normalize, since there might
|
||||
* be an OR subclause in the resulting AND-list.
|
||||
* Note: we rely on pull_ands to build a fresh list,
|
||||
* and not damage the given andlist.
|
||||
*/
|
||||
orclause = and_normalize(pull_ands(lcons(orclause, andlist)));
|
||||
orclauses = lappend(orclauses, orclause);
|
||||
}
|
||||
|
||||
/* pull_ors is needed in case any sub-and_normalize succeeded */
|
||||
return make_orclause(pull_ors(orclauses));
|
||||
}
|
||||
|
||||
@ -1,12 +1,12 @@
|
||||
/*-------------------------------------------------------------------------
|
||||
*
|
||||
* prep.h
|
||||
* prototypes for files in prep.c
|
||||
* prototypes for files in optimizer/prep/
|
||||
*
|
||||
*
|
||||
* Copyright (c) 1994, Regents of the University of California
|
||||
*
|
||||
* $Id: prep.h,v 1.17 1999/07/16 17:07:34 momjian Exp $
|
||||
* $Id: prep.h,v 1.18 1999/09/12 18:08:10 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
@ -20,6 +20,7 @@
|
||||
* prototypes for prepqual.c
|
||||
*/
|
||||
extern List *cnfify(Expr *qual, bool removeAndFlag);
|
||||
extern Expr *dnfify(Expr *qual);
|
||||
|
||||
/*
|
||||
* prototypes for preptlist.c
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user