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Implement IS NOT DISTINCT FROM, update the regression tests and docs.

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Patch from Pavel Stehule, minor fixups by myself.
This commit is contained in:
Neil Conway 2005-12-11 10:54:28 +00:00
parent c10593149a
commit be8100d64e
4 changed files with 57 additions and 6 deletions
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18
doc/src/sgml/func.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.297 2005/12/03 16:45:05 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.298 2005/12/11 10:54:27 neilc Exp $
PostgreSQL documentation
-->
@ -345,16 +345,24 @@ PostgreSQL documentation
<indexterm>
<primary>IS DISTINCT FROM</primary>
</indexterm>
<indexterm>
<primary>IS NOT DISTINCT FROM</primary>
</indexterm>
The ordinary comparison operators yield null (signifying <quote>unknown</>)
when either input is null. Another way to do comparisons is with the
<literal>IS DISTINCT FROM</literal> construct:
<synopsis>
<replaceable>expression</replaceable> IS DISTINCT FROM <replaceable>expression</replaceable>
<replaceable>expression</replaceable> IS NOT DISTINCT FROM <replaceable>expression</replaceable>
</synopsis>
For non-null inputs this is the same as the <literal>&lt;&gt;</> operator.
However, when both inputs are null it will return false, and when just
one input is null it will return true. Thus it effectively acts as though
null were a normal data value, rather than <quote>unknown</>.
For non-null inputs, <literal>IS DISTINCT FROM</literal> this is
the same as the <literal>&lt;&gt;</> operator. However, when both
inputs are null it will return false, and when just one input is
null it will return true. Similarly, <literal>IS NOT DISTINCT
FROM</literal> is identical to <literal>=</literal> for non-null
inputs, returns true when both inputs are null, and false
otherwise. Thus, these constructs effectively act as though null
were a normal data value, rather than <quote>unknown</>.
</para>
<para>

14
src/backend/parser/gram.y
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@ -11,7 +11,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.516 2005/11/28 04:35:31 tgl Exp $
* $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.517 2005/12/11 10:54:27 neilc Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@ -6715,6 +6715,13 @@ a_expr: c_expr { $$ = $1; }
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_DISTINCT, "=", $1, $5);
}
| a_expr IS NOT DISTINCT FROM a_expr %prec IS
{
$$ = (Node *) makeA_Expr(AEXPR_NOT, NIL, NULL,
(Node *) makeSimpleA_Expr(AEXPR_DISTINCT,
"=", $1, $6));
}
| a_expr IS OF '(' type_list ')' %prec IS
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "=", $1, (Node *) $5);
@ -6880,6 +6887,11 @@ b_expr: c_expr
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_DISTINCT, "=", $1, $5);
}
| b_expr IS NOT DISTINCT FROM b_expr %prec IS
{
$$ = (Node *) makeA_Expr(AEXPR_NOT, NIL,
NULL, (Node *) makeSimpleA_Expr(AEXPR_DISTINCT, "=", $1, $6));
}
| b_expr IS OF '(' type_list ')' %prec IS
{
$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "=", $1, (Node *) $5);

25
src/test/regress/expected/select_distinct.out
View File

@ -195,3 +195,28 @@ SELECT null IS DISTINCT FROM null as "no";
f
(1 row)
-- ANSI SQL 2003 form
SELECT 1 IS NOT DISTINCT FROM 2 as "no";
no
----
f
(1 row)
SELECT 2 IS NOT DISTINCT FROM 2 as "yes";
yes
-----
t
(1 row)
SELECT 2 IS NOT DISTINCT FROM null as "no";
no
----
f
(1 row)
SELECT null IS NOT DISTINCT FROM null as "yes";
yes
-----
t
(1 row)

6
src/test/regress/sql/select_distinct.sql
View File

@ -56,3 +56,9 @@ SELECT 1 IS DISTINCT FROM 2 as "yes";
SELECT 2 IS DISTINCT FROM 2 as "no";
SELECT 2 IS DISTINCT FROM null as "yes";
SELECT null IS DISTINCT FROM null as "no";
-- ANSI SQL 2003 form
SELECT 1 IS NOT DISTINCT FROM 2 as "no";
SELECT 2 IS NOT DISTINCT FROM 2 as "yes";
SELECT 2 IS NOT DISTINCT FROM null as "no";
SELECT null IS NOT DISTINCT FROM null as "yes";