From 2119cc0670c90f0c857137d1ca37c99997e31290 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 12 Sep 1999 18:08:17 +0000
Subject: [PATCH] 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.
---
src/backend/optimizer/prep/prepqual.c | 713 ++++++++++++++------------
src/include/optimizer/prep.h | 5 +-
2 files changed, 384 insertions(+), 334 deletions(-)
diff --git a/src/backend/optimizer/prep/prepqual.c b/src/backend/optimizer/prep/prepqual.c
index 974884d8bcc..72e26f35074 100644
--- a/src/backend/optimizer/prep/prepqual.c
+++ b/src/backend/optimizer/prep/prepqual.c
@@ -1,13 +1,13 @@
/*-------------------------------------------------------------------------
*
* prepqual.c
- * Routines for preprocessing the parse tree qualification
+ * Routines for preprocessing qualification expressions
*
* Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.18 1999/09/07 03:47:06 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.19 1999/09/12 18:08:17 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -20,28 +20,33 @@
#include "optimizer/prep.h"
#include "utils/lsyscache.h"
-static Expr *flatten_andors(Expr *qual, bool deep);
+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 *normalize(Expr *qual);
-static List *or_normalize(List *orlist);
-static List *distribute_args(List *item, List *args);
-static List *qual_cleanup(Expr *qual);
-static List *remove_duplicates(List *list);
+static Expr *find_ors(Expr *qual);
+static Expr *or_normalize(List *orlist);
+static Expr *find_ands(Expr *qual);
+static Expr *and_normalize(List *andlist);
/*****************************************************************************
*
- * CNF CONVERSION ROUTINES
+ * CNF/DNF CONVERSION ROUTINES
*
- * NOTES:
- * The basic algorithms for normalizing the qualification are taken
- * from ingres/source/qrymod/norml.c
+ * These routines convert an arbitrary boolean expression into
+ * conjunctive normal form or disjunctive normal form.
*
- * 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.
+ * The result of these routines differs from a "true" CNF/DNF in that
+ * we do not bother to detect common subexpressions; e.g., ("AND" A A)
+ * does not get simplified to A. Testing for identical subexpressions
+ * is a waste of time if the query is written intelligently, and it
+ * takes an unreasonable amount of time if there are many subexpressions
+ * (since it's roughly O(N^2) in the number of subexpressions).
+ *
+ * Because of that restriction, it would be unwise to apply dnfify()
+ * to the result of cnfify() or vice versa. Instead apply both to
+ * the original user-written qual expression.
*
*****************************************************************************/
@@ -54,44 +59,225 @@ static List *remove_duplicates(List *list);
* 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 normal
- * boolean expression is returned.
- *
- * NOTE: this routine is called by the planner (removeAndFlag = true)
- * and from the rule manager (removeAndFlag = false).
- *
+ * 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 = NULL;
+ Expr *newqual;
- if (qual != NULL)
+ 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);
+
+ if (removeAndFlag)
{
- /* Flatten AND and OR groups throughout the tree.
- * This improvement is always worthwhile.
- */
- newqual = flatten_andors(qual, true);
- /* Push down NOTs. We do this only in the top-level boolean
- * expression, without examining arguments of operators/functions.
- */
- newqual = find_nots(newqual);
- /* Pushing NOTs could have brought AND/ORs together, so do
- * another flatten_andors (only in the top level); then normalize.
- */
- newqual = normalize(flatten_andors(newqual, false));
- /* Do we need a flatten here? Anyway, clean up after normalize. */
- newqual = (Expr *) qual_cleanup(flatten_andors(newqual, false));
- /* This flatten is almost surely a waste of time... */
- newqual = flatten_andors(newqual, false);
+ newqual = (Expr *) make_ands_implicit(newqual);
+ }
+
+ return (List *) newqual;
+}
+
+/*
+ * 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.
+ */
+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);
- if (removeAndFlag)
+ return newqual;
+}
+
+/*--------------------
+ * 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)
{
- newqual = (Expr *) make_ands_implicit(newqual);
+ 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;
- return (List *) (newqual);
+ 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;
}
/*
@@ -100,8 +286,7 @@ cnfify(Expr *qual, bool removeAndFlag)
* For 'NOT' clauses, apply push_not() to try to push down the 'NOT'.
* For all other clause types, simply recurse.
*
- * Returns the modified qualification.
- *
+ * Returns the modified qualification. AND/OR flatness is preserved.
*/
static Expr *
find_nots(Expr *qual)
@@ -134,7 +319,7 @@ find_nots(Expr *qual)
foreach(temp, qual->args)
t_list = lappend(t_list, find_nots(lfirst(temp)));
- return make_andclause(t_list);
+ return make_andclause(pull_ands(t_list));
}
else if (or_clause((Node *) qual))
{
@@ -143,7 +328,7 @@ find_nots(Expr *qual)
foreach(temp, qual->args)
t_list = lappend(t_list, find_nots(lfirst(temp)));
- return make_orclause(t_list);
+ return make_orclause(pull_ors(t_list));
}
else if (not_clause((Node *) qual))
return push_nots(get_notclausearg(qual));
@@ -187,17 +372,19 @@ push_nots(Expr *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.
+ /*--------------------
+ * 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(t_list);
+ return make_orclause(pull_ors(t_list));
}
else if (or_clause((Node *) qual))
{
@@ -206,7 +393,7 @@ push_nots(Expr *qual)
foreach(temp, qual->args)
t_list = lappend(t_list, push_nots(lfirst(temp)));
- return make_andclause(t_list);
+ return make_andclause(pull_ands(t_list));
}
else if (not_clause((Node *) qual))
{
@@ -228,20 +415,18 @@ push_nots(Expr *qual)
}
/*
- * normalize
+ * 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))
- * bottom-up.
- * Note that 'or' clauses will always be turned into 'and' clauses
- * if they contain any 'and' subclauses. XXX this is not always
- * an improvement...
*
- * Returns the modified qualification.
+ * 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 *
-normalize(Expr *qual)
+find_ors(Expr *qual)
{
if (qual == NULL)
return NULL;
@@ -249,346 +434,210 @@ normalize(Expr *qual)
/* We used to recurse into opclauses here, but I see no reason to... */
if (and_clause((Node *) qual))
{
- List *t_list = NIL;
+ List *andlist = NIL;
List *temp;
foreach(temp, qual->args)
- t_list = lappend(t_list, normalize(lfirst(temp)));
- return make_andclause(t_list);
+ andlist = lappend(andlist, find_ors(lfirst(temp)));
+ return make_andclause(pull_ands(andlist));
}
else if (or_clause((Node *) qual))
{
- /* XXX - let form, maybe incorrect */
List *orlist = NIL;
- bool has_andclause = false;
List *temp;
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)
- return make_andclause(or_normalize(orlist));
- else
- return make_orclause(orlist);
+ orlist = lappend(orlist, find_ors(lfirst(temp)));
+ return or_normalize(pull_ors(orlist));
}
else if (not_clause((Node *) qual))
- return make_notclause(normalize(get_notclausearg(qual)));
+ return make_notclause(find_ors(get_notclausearg(qual)));
else
return qual;
}
/*
- * qual_cleanup
- * Fix up a qualification by removing duplicate entries (left over from
- * normalization), and by removing 'and' and 'or' clauses which have only
- * one remaining subexpr (e.g., ("AND" A) => A).
+ * 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 modified qualification.
+ * Returns the resulting expression (could be an AND clause, an OR
+ * clause, or maybe even a single subexpression).
*/
-static List *
-qual_cleanup(Expr *qual)
+static Expr *
+or_normalize(List *orlist)
{
- if (qual == NULL)
- return NIL;
+ Expr *distributable = NULL;
+ int num_subclauses = 1;
+ List *andclauses = NIL;
+ List *temp;
- if (is_opclause((Node *) qual))
- {
- Expr *left = (Expr *) get_leftop(qual);
- Expr *right = (Expr *) get_rightop(qual);
+ if (orlist == NIL)
+ return NULL; /* probably can't happen */
+ if (lnext(orlist) == NIL)
+ return lfirst(orlist); /* single-expression OR (can this happen?) */
- if (right)
- return (List *) make_clause(qual->opType, qual->oper,
- lcons(qual_cleanup(left),
- lcons(qual_cleanup(right),
- NIL)));
- else
- return (List *) make_clause(qual->opType, qual->oper,
- lcons(qual_cleanup(left),
- NIL));
- }
- else if (and_clause((Node *) qual))
+ /*
+ * 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 *t_list = NIL;
- List *temp;
- List *new_and_args;
-
- foreach(temp, qual->args)
- t_list = lappend(t_list, qual_cleanup(lfirst(temp)));
+ Expr *clause = lfirst(temp);
- new_and_args = remove_duplicates(t_list);
+ if (and_clause((Node *) clause))
+ {
+ int nclauses = length(clause->args);
- if (length(new_and_args) > 1)
- return (List *) make_andclause(new_and_args);
- else
- return lfirst(new_and_args);
+ if (nclauses > num_subclauses)
+ {
+ distributable = clause;
+ num_subclauses = nclauses;
+ }
+ }
}
- else if (or_clause((Node *) qual))
- {
- List *t_list = NIL;
- List *temp;
- List *new_or_args;
- foreach(temp, qual->args)
- t_list = lappend(t_list, qual_cleanup(lfirst(temp)));
+ /* if there's no suitable AND clause, we can't transform the OR */
+ if (! distributable)
+ return make_orclause(orlist);
- new_or_args = remove_duplicates(t_list);
+ /* 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);
- if (length(new_or_args) > 1)
- return (List *) make_orclause(new_or_args);
- else
- return lfirst(new_or_args);
+ 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);
}
- else if (not_clause((Node *) qual))
- return (List *) make_notclause((Expr *) qual_cleanup((Expr *) get_notclausearg(qual)));
- else
- return (List *) qual;
+
+ /* pull_ands is needed in case any sub-or_normalize succeeded */
+ return make_andclause(pull_ands(andclauses));
}
-/*--------------------
- * flatten_andors
- * Given a qualification, simplify nested AND/OR clauses into flat
- * AND/OR clauses with more arguments.
- *
- * 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 this routine.
+/*
+ * 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))
*
- * If 'deep' is true, we search the whole tree for AND/ORs to simplify;
- * if not, we consider only the top-level AND/OR/NOT structure.
+ * Note that 'and' clauses will always be turned into 'or' clauses
+ * if they contain any 'or' subclauses.
*
- * Returns the rebuilt expr (note original list structure is not touched).
- *--------------------
+ * Returns the modified qualification. AND/OR flatness is preserved.
*/
static Expr *
-flatten_andors(Expr *qual, bool deep)
+find_ands(Expr *qual)
{
if (qual == NULL)
return NULL;
- if (and_clause((Node *) qual))
+ /* We used to recurse into opclauses here, but I see no reason to... */
+ if (or_clause((Node *) qual))
{
- List *out_list = NIL;
- List *arg;
-
- foreach(arg, qual->args)
- {
- Expr *subexpr = flatten_andors((Expr *) lfirst(arg), deep);
+ List *orlist = NIL;
+ List *temp;
- /*
- * 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);
+ foreach(temp, qual->args)
+ orlist = lappend(orlist, find_ands(lfirst(temp)));
+ return make_orclause(pull_ors(orlist));
}
- else if (or_clause((Node *) qual))
+ else if (and_clause((Node *) qual))
{
- List *out_list = NIL;
- List *arg;
-
- foreach(arg, qual->args)
- {
- Expr *subexpr = flatten_andors((Expr *) lfirst(arg), deep);
+ List *andlist = NIL;
+ List *temp;
- /*
- * 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);
+ 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(flatten_andors(get_notclausearg(qual), deep));
- else if (deep && 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, deep),
- lcons(flatten_andors(right, deep),
- NIL)));
- else
- return make_clause(qual->opType, qual->oper,
- lcons(flatten_andors(left, deep),
- NIL));
- }
+ return make_notclause(find_ands(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.
+ * 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.
*
- * Input is the arglist of an OR clause.
- * Returns the rebuilt arglist (note original list structure is not touched).
+ * Returns the resulting expression (could be an AND clause, an OR
+ * clause, or maybe even a single subexpression).
*/
-static List *
-pull_ors(List *orlist)
+static Expr *
+and_normalize(List *andlist)
{
- 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;
-}
+ Expr *distributable = NULL;
+ int num_subclauses = 1;
+ List *orclauses = NIL;
+ List *temp;
-/*
- * 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;
+ if (andlist == NIL)
+ return NULL; /* probably can't happen */
+ if (lnext(andlist) == NIL)
+ return lfirst(andlist); /* single-expression AND (can this happen?) */
- foreach(arg, andlist)
+ /*
+ * 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 *subexpr = (Expr *) lfirst(arg);
+ Expr *clause = lfirst(temp);
- /*
- * 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;
-}
-
-/*
- * 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)))
+ if (or_clause((Node *) clause))
{
- distributable = lfirst(temp);
- break;
- }
- }
- if (distributable)
- new_orlist = LispRemove(distributable, orlist);
+ int nclauses = length(clause->args);
- if (new_orlist)
- {
- return or_normalize(lcons(distribute_args(lfirst(new_orlist),
- ((Expr *) distributable)->args),
- lnext(new_orlist)));
+ if (nclauses > num_subclauses)
+ {
+ distributable = clause;
+ num_subclauses = nclauses;
+ }
+ }
}
- 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 *t_list = NIL;
- List *temp;
+ /* if there's no suitable OR clause, we can't transform the AND */
+ if (! distributable)
+ return make_andclause(andlist);
- if (args == NULL)
- return item;
+ /* 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, args)
+ foreach(temp, distributable->args)
{
- List *n_list;
+ Expr *orclause = lfirst(temp);
- n_list = or_normalize(pull_ors(lcons(item,
- lcons(lfirst(temp),
- NIL))));
- t_list = lappend(t_list, make_orclause(n_list));
+ /* 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);
}
- return (List *) make_andclause(t_list);
-}
-
-/*
- * 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;
+ /* pull_ors is needed in case any sub-and_normalize succeeded */
+ return make_orclause(pull_ors(orclauses));
}
diff --git a/src/include/optimizer/prep.h b/src/include/optimizer/prep.h
index 8e4128b8c60..161419f29d8 100644
--- a/src/include/optimizer/prep.h
+++ b/src/include/optimizer/prep.h
@@ -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
--
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