The SQL standard appears to specify that IS [NOT] NULL's tests of field
nullness are non-recursive, ie, we shouldn't consider that a composite
field with value ROW(NULL,NULL) is null for this purpose.
ExecEvalNullTest got this right, but eval_const_expressions did not,
leading to weird inconsistencies depending on whether the expression
was such that the planner could apply constant folding.
Also, adjust the docs to mention that IS [NOT] DISTINCT FROM NULL can be
used as a substitute test if a simple null check is wanted for a rowtype
argument. That motivated reordering things so that IS [NOT] DISTINCT FROM
is described before IS [NOT] NULL. In HEAD, I went a bit further and added
a table showing all the comparison-related predicates.
Per bug #14235. Back-patch to all supported branches, since it's certainly
undesirable that constant-folding should change the semantics.
Report and patch by Andrew Gierth; assorted wordsmithing and revised
regression test cases by me.
Report: <
20160708024746.1410.57282@wrigleys.postgresql.org>
a nonempty range is always implied.
</para>
+ <para>
+ <indexterm>
+ <primary>IS DISTINCT FROM</primary>
+ </indexterm>
+ <indexterm>
+ <primary>IS NOT DISTINCT FROM</primary>
+ </indexterm>
+ Ordinary comparison operators yield null (signifying <quote>unknown</>),
+ not true or false, when either input is null. For example,
+ <literal>7 = NULL</> yields null, as does <literal>7 <> NULL</>. When
+ this behavior is not suitable, use the
+ <literal>IS <optional> NOT </> DISTINCT FROM</literal> constructs:
+<synopsis>
+<replaceable>a</replaceable> IS DISTINCT FROM <replaceable>b</replaceable>
+<replaceable>a</replaceable> IS NOT DISTINCT FROM <replaceable>b</replaceable>
+</synopsis>
+ For non-null inputs, <literal>IS DISTINCT FROM</literal> is
+ the same as the <literal><></> operator. However, if both
+ inputs are null it returns false, and if only one input is
+ null it returns true. Similarly, <literal>IS NOT DISTINCT
+ FROM</literal> is identical to <literal>=</literal> for non-null
+ inputs, but it returns true when both inputs are null, and false when only
+ one input is null. Thus, these constructs effectively act as though null
+ were a normal data value, rather than <quote>unknown</>.
+ </para>
+
<para>
<indexterm>
<primary>IS NULL</primary>
<literal><replaceable>expression</replaceable> = NULL</literal>
because <literal>NULL</> is not <quote>equal to</quote>
<literal>NULL</>. (The null value represents an unknown value,
- and it is not known whether two unknown values are equal.) This
- behavior conforms to the SQL standard.
+ and it is not known whether two unknown values are equal.)
</para>
<tip>
</para>
</tip>
- <note>
<para>
If the <replaceable>expression</replaceable> is row-valued, then
<literal>IS NULL</> is true when the row expression itself is null
<literal>IS NOT NULL</> is true when the row expression itself is non-null
and all the row's fields are non-null. Because of this behavior,
<literal>IS NULL</> and <literal>IS NOT NULL</> do not always return
- inverse results for row-valued expressions, i.e., a row-valued
- expression that contains both NULL and non-null values will return false
- for both tests.
- This definition conforms to the SQL standard, and is a change from the
- inconsistent behavior exhibited by <productname>PostgreSQL</productname>
- versions prior to 8.2.
- </para>
- </note>
-
- <para>
- <indexterm>
- <primary>IS DISTINCT FROM</primary>
- </indexterm>
- <indexterm>
- <primary>IS NOT DISTINCT FROM</primary>
- </indexterm>
- Ordinary comparison operators yield null (signifying <quote>unknown</>),
- not true or false, when either input is null. For example,
- <literal>7 = NULL</> yields null. When this behavior is not suitable,
- use the
- <literal>IS <optional> NOT </> DISTINCT FROM</literal> constructs:
-<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, <literal>IS DISTINCT FROM</literal> is
- the same as the <literal><></> operator. However, if both
- inputs are null it returns false, and if only one input is
- null it returns true. Similarly, <literal>IS NOT DISTINCT
- FROM</literal> is identical to <literal>=</literal> for non-null
- inputs, but it returns true when both inputs are null, and false when only
- one input is null. Thus, these constructs effectively act as though null
- were a normal data value, rather than <quote>unknown</>.
+ inverse results for row-valued expressions; in particular, a row-valued
+ expression that contains both null and non-null fields will return false
+ for both tests. In some cases, it may be preferable to
+ write <replaceable>row</replaceable> <literal>IS DISTINCT FROM NULL</>
+ or <replaceable>row</replaceable> <literal>IS NOT DISTINCT FROM NULL</>,
+ which will simply check whether the overall row value is null without any
+ additional tests on the row fields.
</para>
<para>
if (ntest->argisrow && !(*isNull))
{
+ /*
+ * The SQL standard defines IS [NOT] NULL for a non-null rowtype
+ * argument as:
+ *
+ * "R IS NULL" is true if every field is the null value.
+ *
+ * "R IS NOT NULL" is true if no field is the null value.
+ *
+ * This definition is (apparently intentionally) not recursive; so our
+ * tests on the fields are primitive attisnull tests, not recursive
+ * checks to see if they are all-nulls or no-nulls rowtypes.
+ *
+ * The standard does not consider the possibility of zero-field rows,
+ * but here we consider them to vacuously satisfy both predicates.
+ */
HeapTupleHeader tuple;
Oid tupType;
int32 tupTypmod;
arg = eval_const_expressions_mutator((Node *) ntest->arg,
context);
- if (arg && IsA(arg, RowExpr))
+ if (ntest->argisrow && arg && IsA(arg, RowExpr))
{
/*
* We break ROW(...) IS [NOT] NULL into separate tests on its
List *newargs = NIL;
ListCell *l;
- Assert(ntest->argisrow);
-
foreach(l, rarg->args)
{
Node *relem = (Node *) lfirst(l);
return makeBoolConst(false, false);
continue;
}
+
+ /*
+ * Else, make a scalar (argisrow == false) NullTest for this
+ * field. Scalar semantics are required because IS [NOT] NULL
+ * doesn't recurse; see comments in ExecEvalNullTest().
+ */
newntest = makeNode(NullTest);
newntest->arg = (Expr *) relem;
newntest->nulltesttype = ntest->nulltesttype;
- newntest->argisrow = type_is_rowtype(exprType(relem));
+ newntest->argisrow = false;
newargs = lappend(newargs, newntest);
}
/* If all the inputs were constants, result is TRUE */
ERROR: could not identify column "text" in record data type
LINE 1: select (row('Jim', 'Beam')).text;
^
+--
+-- IS [NOT] NULL should not recurse into nested composites (bug #14235)
+--
+explain (verbose, costs off)
+select r, r is null as isnull, r is not null as isnotnull
+from (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) ) r(a,b);
+ QUERY PLAN
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Values Scan on "*VALUES*"
+ Output: ROW("*VALUES*".column1, "*VALUES*".column2), (("*VALUES*".column1 IS NULL) AND ("*VALUES*".column2 IS NULL)), (("*VALUES*".column1 IS NOT NULL) AND ("*VALUES*".column2 IS NOT NULL))
+(2 rows)
+
+select r, r is null as isnull, r is not null as isnotnull
+from (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) ) r(a,b);
+ r | isnull | isnotnull
+-------------+--------+-----------
+ (1,"(1,2)") | f | t
+ (1,"(,)") | f | t
+ (1,) | f | f
+ (,"(1,2)") | f | f
+ (,"(,)") | f | f
+ (,) | t | f
+(6 rows)
+
+explain (verbose, costs off)
+with r(a,b) as
+ (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) )
+select r, r is null as isnull, r is not null as isnotnull from r;
+ QUERY PLAN
+----------------------------------------------------------
+ CTE Scan on r
+ Output: r.*, (r.* IS NULL), (r.* IS NOT NULL)
+ CTE r
+ -> Values Scan on "*VALUES*"
+ Output: "*VALUES*".column1, "*VALUES*".column2
+(5 rows)
+
+with r(a,b) as
+ (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) )
+select r, r is null as isnull, r is not null as isnotnull from r;
+ r | isnull | isnotnull
+-------------+--------+-----------
+ (1,"(1,2)") | f | t
+ (1,"(,)") | f | t
+ (1,) | f | f
+ (,"(1,2)") | f | f
+ (,"(,)") | f | f
+ (,) | t | f
+(6 rows)
+
select (row('Jim', 'Beam'))::text;
select text(row('Jim', 'Beam')); -- error
select (row('Jim', 'Beam')).text; -- error
+
+--
+-- IS [NOT] NULL should not recurse into nested composites (bug #14235)
+--
+
+explain (verbose, costs off)
+select r, r is null as isnull, r is not null as isnotnull
+from (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) ) r(a,b);
+
+select r, r is null as isnull, r is not null as isnotnull
+from (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) ) r(a,b);
+
+explain (verbose, costs off)
+with r(a,b) as
+ (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) )
+select r, r is null as isnull, r is not null as isnotnull from r;
+
+with r(a,b) as
+ (values (1,row(1,2)), (1,row(null,null)), (1,null),
+ (null,row(1,2)), (null,row(null,null)), (null,null) )
+select r, r is null as isnull, r is not null as isnotnull from r;
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