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-/*-------------------------------------------------------------------------
- *
- * prepqual.c
- * Routines for preprocessing qualification expressions
- *
- * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- *
- * IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.32 2002/06/20 20:29:31 momjian Exp $
- *
- *-------------------------------------------------------------------------
- */
-#include <sys/types.h>
-
-#include "postgres.h"
-
-#include "nodes/makefuncs.h"
-#include "optimizer/clauses.h"
-#include "optimizer/prep.h"
-#include "utils/lsyscache.h"
-
-static Expr *flatten_andors(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 *find_ors(Expr *qual);
-static Expr *or_normalize(List *orlist);
-static Expr *find_ands(Expr *qual);
-static Expr *and_normalize(List *andlist);
-static Expr *qual_cleanup(Expr *qual);
-static List *remove_duplicates(List *list);
-static void count_bool_nodes(Expr *qual, double *nodes,
- double *cnfnodes, double *dnfnodes);
-
-/*****************************************************************************
- *
- * CNF/DNF CONVERSION ROUTINES
- *
- * These routines convert an arbitrary boolean expression into
- * conjunctive normal form or disjunctive normal form.
- *
- * Normalization is only carried out in the top AND/OR/NOT portion
- * of the given tree; we do not attempt to normalize boolean expressions
- * that may appear as arguments of operators or functions in the tree.
- *
- * Query qualifications (WHERE clauses) are ordinarily transformed into
- * CNF, ie, AND-of-ORs form, because then the optimizer can use any one
- * of the independent AND clauses as a filtering qualification. However,
- * quals that are naturally expressed as OR-of-ANDs can suffer an
- * exponential growth in size in this transformation, so we also consider
- * converting to DNF (OR-of-ANDs), and we may also leave well enough alone
- * if both transforms cause unreasonable growth. The OR-of-ANDs format
- * is useful for indexscan implementation, so we prefer that format when
- * there is just one relation involved.
- *
- * canonicalize_qual() does "smart" conversion to either CNF or DNF, per
- * the above considerations, while cnfify() and dnfify() simply perform
- * the demanded transformation. The latter two may become dead code
- * eventually.
- *****************************************************************************/
-
-
-/*
- * canonicalize_qual
- * Convert a qualification to the most useful normalized form.
- *
- * Returns the modified qualification.
- *
- * If 'removeAndFlag' is true then it removes explicit AND at the top level,
- * producing a list of implicitly-ANDed conditions. Otherwise, a regular
- * boolean expression is returned. Since most callers pass 'true', we
- * prefer to declare the result as List *, not Expr *.
- *
- * XXX This code could be much smarter, at the cost of also being slower,
- * if we tried to compute selectivities and/or see whether there are
- * actually indexes to support an indexscan implementation of a DNF qual.
- * We could even try converting the CNF clauses that mention a single
- * relation into a single DNF clause to see if that looks cheaper to
- * implement. For now, though, we just try to avoid doing anything
- * quite as stupid as unconditionally converting to CNF was...
- */
-List *
-canonicalize_qual(Expr *qual, bool removeAndFlag)
-{
- Expr *newqual;
- double nodes,
- cnfnodes,
- dnfnodes;
- bool cnfok,
- dnfok;
-
- if (qual == NULL)
- return NIL;
-
- /*
- * Flatten AND and OR groups throughout the tree. This improvement is
- * always worthwhile, so do it unconditionally.
- */
- qual = flatten_andors(qual);
-
- /*
- * Push down NOTs. We do this only in the top-level boolean
- * expression, without examining arguments of operators/functions.
- * Even so, it might not be a win if we are unable to find negators
- * for all the operators involved; perhaps we should compare before-
- * and-after tree sizes?
- */
- newqual = find_nots(qual);
-
- /*
- * Choose whether to convert to CNF, or DNF, or leave well enough
- * alone.
- *
- * We make an approximate estimate of the number of bottom-level nodes
- * that will appear in the CNF and DNF forms of the query.
- */
- count_bool_nodes(newqual, &nodes, &cnfnodes, &dnfnodes);
-
- /*
- * First heuristic is to forget about *both* normal forms if there are
- * a huge number of terms in the qual clause. This would only happen
- * with machine-generated queries, presumably; and most likely such a
- * query is already in either CNF or DNF.
- */
- cnfok = dnfok = true;
- if (nodes >= 500.0)
- cnfok = dnfok = false;
-
- /*
- * Second heuristic is to forget about either CNF or DNF if it shows
- * unreasonable growth compared to the original form of the qual,
- * where we define "unreasonable" a tad arbitrarily as 4x more
- * operators.
- */
- if (cnfnodes >= 4.0 * nodes)
- cnfok = false;
- if (dnfnodes >= 4.0 * nodes)
- dnfok = false;
-
- /*
- * Third heuristic is to prefer DNF if top level is already an OR, and
- * only one relation is mentioned, and DNF is no larger than the CNF
- * representation. (Pretty shaky; can we improve on this?)
- */
- if (cnfok && dnfok && dnfnodes <= cnfnodes &&
- or_clause((Node *) newqual) &&
- NumRelids((Node *) newqual) == 1)
- cnfok = false;
-
- /*
- * Otherwise, we prefer CNF.
- *
- * XXX obviously, these rules could be improved upon.
- */
- if (cnfok)
- {
- /*
- * Normalize into conjunctive normal form, and clean up the
- * result.
- */
- newqual = qual_cleanup(find_ors(newqual));
- }
- else if (dnfok)
- {
- /*
- * Normalize into disjunctive normal form, and clean up the
- * result.
- */
- newqual = qual_cleanup(find_ands(newqual));
- }
-
- /* Convert to implicit-AND list if requested */
- if (removeAndFlag)
- newqual = (Expr *) make_ands_implicit(newqual);
-
- return (List *) newqual;
-}
-
-/*
- * cnfify
- * Convert a qualification to conjunctive normal form by applying
- * successive normalizations.
- *
- * Returns the modified qualification.
- *
- * If 'removeAndFlag' is true then it removes explicit AND at the top level,
- * producing a list of implicitly-ANDed conditions. Otherwise, a regular
- * boolean expression is returned. Since most callers pass 'true', we
- * prefer to declare the result as List *, not Expr *.
- */
-List *
-cnfify(Expr *qual, bool removeAndFlag)
-{
- Expr *newqual;
-
- if (qual == NULL)
- return NIL;
-
- /*
- * Flatten AND and OR groups throughout the tree. This improvement is
- * always worthwhile.
- */
- newqual = flatten_andors(qual);
-
- /*
- * Push down NOTs. We do this only in the top-level boolean
- * expression, without examining arguments of operators/functions.
- */
- newqual = find_nots(newqual);
- /* Normalize into conjunctive normal form. */
- newqual = find_ors(newqual);
- /* Clean up the result. */
- newqual = qual_cleanup(newqual);
-
- if (removeAndFlag)
- newqual = (Expr *) make_ands_implicit(newqual);
-
- return (List *) newqual;
-}
-
-#ifdef NOT_USED
-/*
- * dnfify
- * Convert a qualification to disjunctive normal form by applying
- * successive normalizations.
- *
- * Returns the modified qualification.
- *
- * We do not offer a 'removeOrFlag' in this case; the usages are
- * different.
- */
-static Expr *
-dnfify(Expr *qual)
-{
- Expr *newqual;
-
- if (qual == NULL)
- return NULL;
-
- /*
- * Flatten AND and OR groups throughout the tree. This improvement is
- * always worthwhile.
- */
- newqual = flatten_andors(qual);
-
- /*
- * Push down NOTs. We do this only in the top-level boolean
- * expression, without examining arguments of operators/functions.
- */
- newqual = find_nots(newqual);
- /* Normalize into disjunctive normal form. */
- newqual = find_ands(newqual);
- /* Clean up the result. */
- newqual = qual_cleanup(newqual);
-
- return newqual;
-}
-#endif
-
-/*--------------------
- * The parser regards AND and OR as purely binary operators, so a qual like
- * (A = 1) OR (A = 2) OR (A = 3) ...
- * will produce a nested parsetree
- * (OR (A = 1) (OR (A = 2) (OR (A = 3) ...)))
- * In reality, the optimizer and executor regard AND and OR as n-argument
- * operators, so this tree can be flattened to
- * (OR (A = 1) (A = 2) (A = 3) ...)
- * which is the responsibility of the routines below.
- *
- * flatten_andors() does the basic transformation with no initial assumptions.
- * pull_ands() and pull_ors() are used to maintain flatness of the AND/OR
- * tree after local transformations that might introduce nested AND/ORs.
- *--------------------
- */
-
-/*--------------------
- * flatten_andors
- * Given a qualification, simplify nested AND/OR clauses into flat
- * AND/OR clauses with more arguments.
- *
- * Returns the rebuilt expr (note original list structure is not touched).
- *--------------------
- */
-static Expr *
-flatten_andors(Expr *qual)
-{
- if (qual == NULL)
- return NULL;
-
- if (and_clause((Node *) qual))
- {
- List *out_list = NIL;
- List *arg;
-
- foreach(arg, qual->args)
- {
- Expr *subexpr = flatten_andors((Expr *) lfirst(arg));
-
- /*
- * Note: we can destructively nconc the subexpression's
- * arglist because we know the recursive invocation of
- * flatten_andors will have built a new arglist not shared
- * with any other expr. Otherwise we'd need a listCopy here.
- */
- if (and_clause((Node *) subexpr))
- out_list = nconc(out_list, subexpr->args);
- else
- out_list = lappend(out_list, subexpr);
- }
- return make_andclause(out_list);
- }
- else if (or_clause((Node *) qual))
- {
- List *out_list = NIL;
- List *arg;
-
- foreach(arg, qual->args)
- {
- Expr *subexpr = flatten_andors((Expr *) lfirst(arg));
-
- /*
- * Note: we can destructively nconc the subexpression's
- * arglist because we know the recursive invocation of
- * flatten_andors will have built a new arglist not shared
- * with any other expr. Otherwise we'd need a listCopy here.
- */
- if (or_clause((Node *) subexpr))
- out_list = nconc(out_list, subexpr->args);
- else
- out_list = lappend(out_list, subexpr);
- }
- return make_orclause(out_list);
- }
- else if (not_clause((Node *) qual))
- return make_notclause(flatten_andors(get_notclausearg(qual)));
- else if (is_opclause((Node *) qual))
- {
- Expr *left = (Expr *) get_leftop(qual);
- Expr *right = (Expr *) get_rightop(qual);
-
- if (right)
- return make_clause(qual->opType, qual->oper,
- lcons(flatten_andors(left),
- lcons(flatten_andors(right),
- NIL)));
- else
- return make_clause(qual->opType, qual->oper,
- lcons(flatten_andors(left),
- NIL));
- }
- 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.
- *
- * Input is the arglist of an OR clause.
- * Returns the rebuilt arglist (note original list structure is not touched).
- */
-static List *
-pull_ors(List *orlist)
-{
- List *out_list = NIL;
- List *arg;
-
- foreach(arg, orlist)
- {
- Expr *subexpr = (Expr *) lfirst(arg);
-
- /*
- * Note: we can destructively nconc the subexpression's arglist
- * because we know the recursive invocation of pull_ors will have
- * built a new arglist not shared with any other expr. Otherwise
- * we'd need a listCopy here.
- */
- if (or_clause((Node *) subexpr))
- out_list = nconc(out_list, pull_ors(subexpr->args));
- else
- out_list = lappend(out_list, subexpr);
- }
- return out_list;
-}
-
-/*
- * 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)
-{
- List *out_list = NIL;
- List *arg;
-
- foreach(arg, andlist)
- {
- Expr *subexpr = (Expr *) lfirst(arg);
-
- /*
- * Note: we can destructively nconc the subexpression's arglist
- * because we know the recursive invocation of pull_ands will have
- * built a new arglist not shared with any other expr. Otherwise
- * we'd need a listCopy here.
- */
- if (and_clause((Node *) subexpr))
- out_list = nconc(out_list, pull_ands(subexpr->args));
- else
- out_list = lappend(out_list, subexpr);
- }
- return out_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 Expr *
-find_nots(Expr *qual)
-{
- if (qual == NULL)
- return NULL;
-
-#ifdef NOT_USED
- /* recursing into operator expressions is probably not worth it. */
- if (is_opclause((Node *) qual))
- {
- 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));
- }
-#endif
- if (and_clause((Node *) qual))
- {
- 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,
- oper->opretset);
-
- 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
- {
- /*
- * We don't know how to negate anything else, place a 'not' at
- * this level.
- */
- return make_notclause(qual);
- }
-}
-
-/*
- * 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))
- *
- * 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 Expr *
-find_ors(Expr *qual)
-{
- 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 (orlist == NIL)
- return NULL; /* probably can't happen */
- if (lnext(orlist) == NIL)
- return lfirst(orlist); /* single-expression OR (can this happen?) */
-
- /*
- * 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)
- {
- Expr *clause = lfirst(temp);
-
- if (and_clause((Node *) clause))
- {
- int nclauses = length(clause->args);
-
- if (nclauses > num_subclauses)
- {
- distributable = clause;
- num_subclauses = nclauses;
- }
- }
- }
-
- /* 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);
- List *neworlist;
-
- /*
- * We are going to insert the orlist into multiple places in the
- * result expression. For most expression types, it'd be OK to
- * just have multiple links to the same subtree, but this fails
- * badly for SubLinks (and perhaps other cases?). For safety, we
- * make a distinct copy for each place the orlist is inserted.
- */
- if (lnext(temp) == NIL)
- neworlist = orlist; /* can use original tree at the end */
- else
- neworlist = copyObject(orlist);
-
- /*
- * 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.
- */
- andclause = or_normalize(pull_ors(lcons(andclause, neworlist)));
- andclauses = lappend(andclauses, andclause);
- }
-
- /* pull_ands is needed in case any sub-or_normalize succeeded */
- return make_andclause(pull_ands(andclauses));
-}
-
-/*
- * 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 Expr *
-find_ands(Expr *qual)
-{
- if (qual == NULL)
- return NULL;
-
- /* We used to recurse into opclauses here, but I see no reason to... */
- if (or_clause((Node *) qual))
- {
- List *orlist = NIL;
- List *temp;
-
- foreach(temp, qual->args)
- orlist = lappend(orlist, find_ands(lfirst(temp)));
- return make_orclause(pull_ors(orlist));
- }
- 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);
- List *newandlist;
-
- /*
- * We are going to insert the andlist into multiple places in the
- * result expression. For most expression types, it'd be OK to
- * just have multiple links to the same subtree, but this fails
- * badly for SubLinks (and perhaps other cases?). For safety, we
- * make a distinct copy for each place the andlist is inserted.
- */
- if (lnext(temp) == NIL)
- newandlist = andlist; /* can use original tree at the
- * end */
- else
- newandlist = copyObject(andlist);
-
- /*
- * 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.
- */
- orclause = and_normalize(pull_ands(lcons(orclause, newandlist)));
- orclauses = lappend(orclauses, orclause);
- }
-
- /* pull_ors is needed in case any sub-and_normalize succeeded */
- return make_orclause(pull_ors(orclauses));
-}
-
-/*
- * qual_cleanup
- * Fix up a qualification by removing duplicate entries (which could be
- * created during normalization, if identical subexpressions from different
- * parts of the tree are brought together). Also, check for AND and OR
- * clauses with only one remaining subexpression, and simplify.
- *
- * Returns the modified qualification.
- */
-static Expr *
-qual_cleanup(Expr *qual)
-{
- if (qual == NULL)
- return NULL;
-
- if (and_clause((Node *) qual))
- {
- List *andlist = NIL;
- List *temp;
-
- foreach(temp, qual->args)
- andlist = lappend(andlist, qual_cleanup(lfirst(temp)));
-
- andlist = remove_duplicates(pull_ands(andlist));
-
- if (length(andlist) > 1)
- return make_andclause(andlist);
- else
- return lfirst(andlist);
- }
- else if (or_clause((Node *) qual))
- {
- List *orlist = NIL;
- List *temp;
-
- foreach(temp, qual->args)
- orlist = lappend(orlist, qual_cleanup(lfirst(temp)));
-
- orlist = remove_duplicates(pull_ors(orlist));
-
- if (length(orlist) > 1)
- return make_orclause(orlist);
- else
- return lfirst(orlist);
- }
- else if (not_clause((Node *) qual))
- return make_notclause(qual_cleanup(get_notclausearg(qual)));
- else
- return qual;
-}
-
-/*
- * remove_duplicates
- */
-static List *
-remove_duplicates(List *list)
-{
- List *result = NIL;
- List *i;
-
- if (length(list) <= 1)
- return list;
-
- foreach(i, list)
- {
- if (!member(lfirst(i), result))
- result = lappend(result, lfirst(i));
- }
- return result;
-}
-
-/*
- * count_bool_nodes
- * Support for heuristics in canonicalize_qual(): count the
- * number of nodes that are inputs to the top level AND/OR/NOT
- * part of a qual tree, and estimate how many nodes will appear
- * in the CNF'ified or DNF'ified equivalent of the expression.
- *
- * This is just an approximate calculation; it doesn't deal with NOTs
- * very well, and of course it cannot detect possible simplifications
- * from eliminating duplicate subclauses. The idea is just to cheaply
- * determine whether CNF will be markedly worse than DNF or vice versa.
- *
- * The counts/estimates are represented as doubles to avoid risk of overflow.
- */
-static void
-count_bool_nodes(Expr *qual,
- double *nodes,
- double *cnfnodes,
- double *dnfnodes)
-{
- List *temp;
- double subnodes,
- subcnfnodes,
- subdnfnodes;
-
- if (and_clause((Node *) qual))
- {
- *nodes = *cnfnodes = 0.0;
- *dnfnodes = 1.0; /* DNF nodes will be product of sub-counts */
-
- foreach(temp, qual->args)
- {
- count_bool_nodes(lfirst(temp),
- &subnodes, &subcnfnodes, &subdnfnodes);
- *nodes += subnodes;
- *cnfnodes += subcnfnodes;
- *dnfnodes *= subdnfnodes;
- }
-
- /*
- * we could get dnfnodes < cnfnodes here, if all the sub-nodes are
- * simple ones with count 1. Make sure dnfnodes isn't too small.
- */
- if (*dnfnodes < *cnfnodes)
- *dnfnodes = *cnfnodes;
- }
- else if (or_clause((Node *) qual))
- {
- *nodes = *dnfnodes = 0.0;
- *cnfnodes = 1.0; /* CNF nodes will be product of sub-counts */
-
- foreach(temp, qual->args)
- {
- count_bool_nodes(lfirst(temp),
- &subnodes, &subcnfnodes, &subdnfnodes);
- *nodes += subnodes;
- *cnfnodes *= subcnfnodes;
- *dnfnodes += subdnfnodes;
- }
-
- /*
- * we could get cnfnodes < dnfnodes here, if all the sub-nodes are
- * simple ones with count 1. Make sure cnfnodes isn't too small.
- */
- if (*cnfnodes < *dnfnodes)
- *cnfnodes = *dnfnodes;
- }
- else if (not_clause((Node *) qual))
- {
- count_bool_nodes(get_notclausearg(qual),
- nodes, cnfnodes, dnfnodes);
- }
- else if (contain_subplans((Node *) qual))
- {
- /*
- * charge extra for subexpressions containing sub-SELECTs, to
- * discourage us from rearranging them in a way that might
- * generate N copies of a subselect rather than one. The magic
- * constant here interacts with the "4x maximum growth" heuristic
- * in canonicalize_qual().
- */
- *nodes = 1.0;
- *cnfnodes = *dnfnodes = 25.0;
- }
- else
- {
- /* anything else counts 1 for my purposes */
- *nodes = *cnfnodes = *dnfnodes = 1.0;
- }
-}
generated by cgit v1.2.3 (git 2.46.0) at 2025-09-05 10:21:01 +0000