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[email protected]>
a nonempty range is always implied.
+
+
+
+
+ Ordinary comparison operators yield null (signifying unknown),
+ not true or false, when either input is null. For example,
+ 7 = NULL yields null, as does 7 <> NULL. When
+ this behavior is not suitable, use the
+ IS NOT DISTINCT FROM constructs:
+
+a IS DISTINCT FROM b
+a IS NOT DISTINCT FROM b
+
+ For non-null inputs, IS DISTINCT FROM is
+ the same as the <> operator. However, if both
+ inputs are null it returns false, and if only one input is
+ null it returns true. Similarly, IS NOT DISTINCT
+ FROM is identical to = 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 unknown.
+
+
expression = NULL
because NULL is not equal to
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.)
-
If the expression is row-valued, then
IS NULL is true when the row expression itself is null
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,
IS NULL and 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
PostgreSQL- versions prior to 8.2.
-
-
-
-
-
-
-
- Ordinary comparison operators yield null (signifying unknown),
- not true or false, when either input is null. For example,
- 7 = NULL yields null, as does 7 <> NULL. When
- this behavior is not suitable, use the
- IS NOT DISTINCT FROM constructs:
-
-expression IS DISTINCT FROM expression
-expression IS NOT DISTINCT FROM expression
-
- For non-null inputs, IS DISTINCT FROM is
- the same as the <> operator. However, if both
- inputs are null it returns false, and if only one input is
- null it returns true. Similarly, IS NOT DISTINCT
- FROM is identical to = 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 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 row IS DISTINCT FROM NULL
+ or row IS NOT DISTINCT FROM NULL,
+ which will simply check whether the overall row value is null without any
+ additional tests on the row fields.
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
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;
newntest->location = ntest->location;
newargs = lappend(newargs, newntest);
}
{"q2":0,"q1":0}
(3 rows)
+--
+-- 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)
+
create temp table tt2 () inherits(tt1);
insert into tt2 values(0,0);
select row_to_json(r) from (select q2,q1 from tt1 offset 0) r;
+
+--
+-- 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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