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Teach simplify_boolean_equality to simplify the forms foo <> true and

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foo <> false, along with its previous duties of simplifying foo = true
and foo = false.  (All of these are equivalent to just foo or NOT foo
as the case may be.)  It's not clear how often this is really useful;
but it costs almost nothing to do, and it seems some people think we
should be smart about such cases.  Per recent bug report.
This commit is contained in:
Tom Lane
2009-07-20 00:24:30 +00:00
parent 400e2c9344
commit 31d1f23302
2 changed files with 42 additions and 17 deletions
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56
src/backend/optimizer/util/clauses.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.277 2009/06/11 14:48:59 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.278 2009/07/20 00:24:30 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@ -92,7 +92,7 @@ static List *simplify_or_arguments(List *args,
static List *simplify_and_arguments(List *args,
eval_const_expressions_context *context,
bool *haveNull, bool *forceFalse);
static Expr *simplify_boolean_equality(List *args);
static Expr *simplify_boolean_equality(Oid opno, List *args);
static Expr *simplify_function(Oid funcid,
Oid result_type, int32 result_typmod, List **args,
bool allow_inline,
@ -2186,12 +2186,14 @@ eval_const_expressions_mutator(Node *node,
return (Node *) simple;
/*
* If the operator is boolean equality, we know how to simplify cases
* involving one constant and one non-constant argument.
* If the operator is boolean equality or inequality, we know how to
* simplify cases involving one constant and one non-constant
* argument.
*/
if (expr->opno == BooleanEqualOperator)
if (expr->opno == BooleanEqualOperator ||
expr->opno == BooleanNotEqualOperator)
{
simple = simplify_boolean_equality(args);
simple = simplify_boolean_equality(expr->opno, args);
if (simple) /* successfully simplified it */
return (Node *) simple;
}
@ -3165,21 +3167,23 @@ simplify_and_arguments(List *args,
/*
* Subroutine for eval_const_expressions: try to simplify boolean equality
* or inequality condition
*
* Input is the list of simplified arguments to the operator.
* Inputs are the operator OID and the simplified arguments to the operator.
* Returns a simplified expression if successful, or NULL if cannot
* simplify the expression.
*
* The idea here is to reduce "x = true" to "x" and "x = false" to "NOT x".
* The idea here is to reduce "x = true" to "x" and "x = false" to "NOT x",
* or similarly "x <> true" to "NOT x" and "x <> false" to "x".
* This is only marginally useful in itself, but doing it in constant folding
* ensures that we will recognize the two forms as being equivalent in, for
* ensures that we will recognize these forms as being equivalent in, for
* example, partial index matching.
*
* We come here only if simplify_function has failed; therefore we cannot
* see two constant inputs, nor a constant-NULL input.
*/
static Expr *
simplify_boolean_equality(List *args)
simplify_boolean_equality(Oid opno, List *args)
{
Expr *leftop;
Expr *rightop;
@ -3190,18 +3194,38 @@ simplify_boolean_equality(List *args)
if (leftop && IsA(leftop, Const))
{
Assert(!((Const *) leftop)->constisnull);
if (DatumGetBool(((Const *) leftop)->constvalue))
return rightop; /* true = foo */
if (opno == BooleanEqualOperator)
{
if (DatumGetBool(((Const *) leftop)->constvalue))
return rightop; /* true = foo */
else
return make_notclause(rightop); /* false = foo */
}
else
return make_notclause(rightop); /* false = foo */
{
if (DatumGetBool(((Const *) leftop)->constvalue))
return make_notclause(rightop); /* true <> foo */
else
return rightop; /* false <> foo */
}
}
if (rightop && IsA(rightop, Const))
{
Assert(!((Const *) rightop)->constisnull);
if (DatumGetBool(((Const *) rightop)->constvalue))
return leftop; /* foo = true */
if (opno == BooleanEqualOperator)
{
if (DatumGetBool(((Const *) rightop)->constvalue))
return leftop; /* foo = true */
else
return make_notclause(leftop); /* foo = false */
}
else
return make_notclause(leftop); /* foo = false */
{
if (DatumGetBool(((Const *) rightop)->constvalue))
return make_notclause(leftop); /* foo <> true */
else
return leftop; /* foo <> false */
}
}
return NULL;
}