MDEV-16722: Assertion `type() != NULL_ITEM' failed

We hit this assert during the create of a temporary table field
because the current code does not handle the case when the value
of the NAME_CONST function is NULL.
Fixed this by allowing creation of temporary table fields even
for the case when NAME_CONST returns NULL value.
Introduced tmp_table_field_from_field_type_maybe_null() function
in Item class so both Item_basic_value and Item_name_const can use it.
Introduced a virtual method get_func_item() in the Item class.

mysql-test/main/win.result

@@ -3334,3 +3334,14 @@ d	x
 00:00:01	00:00:02
 00:00:02	NULL
 DROP TABLE t1;
+#
+# MDEV-16722: Assertion `type() != NULL_ITEM' failed
+#
+create table t1 (a int);
+insert into t1 values (1),(2),(3);
+SELECT  row_number() OVER (order by a) FROM t1  order by NAME_CONST('myname',NULL);
+row_number() OVER (order by a)
+1
+2
+3
+drop table t1;

mysql-test/main/win.test

@@ -2100,3 +2100,12 @@ CREATE TABLE t1 (d time);
 INSERT INTO t1 VALUES ('00:00:01'),('00:00:02');
 SELECT *, LEAD(d) OVER (ORDER BY d) AS x FROM t1;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-16722: Assertion `type() != NULL_ITEM' failed
+--echo #
+
+create table t1 (a int);
+insert into t1 values (1),(2),(3);
+SELECT  row_number() OVER (order by a) FROM t1  order by NAME_CONST('myname',NULL);
+drop table t1;

sql/item.cc

@@ -1960,7 +1960,6 @@ Item_name_const::Item_name_const(THD *thd, Item *name_arg, Item *val):
   Item_fixed_hybrid(thd), value_item(val), name_item(name_arg)
 {
   Item::maybe_null= TRUE;
-  valid_args= true;
   if (!name_item->basic_const_item())
     goto err;
 
@@ -1979,7 +1978,6 @@ Item_name_const::Item_name_const(THD *thd, Item *name_arg, Item *val):
   }
 
 err:
-  valid_args= false;
   my_error(ER_WRONG_ARGUMENTS, MYF(0), "NAME_CONST");
 }
 
@@ -1987,24 +1985,16 @@ err:
 Item::Type Item_name_const::type() const
 {
   /*
-    As 
-    1. one can try to create the Item_name_const passing non-constant 
-    arguments, although it's incorrect and 
-    2. the type() method can be called before the fix_fields() to get
-    type information for a further type cast, e.g. 
-    if (item->type() == FIELD_ITEM) 
-      ((Item_field *) item)->... 
-    we return NULL_ITEM in the case to avoid wrong casting.
 
-    valid_args guarantees value_item->basic_const_item(); if type is
-    FUNC_ITEM, then we have a fudged item_func_neg() on our hands
-    and return the underlying type.
+    We are guarenteed that value_item->basic_const_item(), if not
+    an error is thrown that WRONG ARGUMENTS are supplied to
+    NAME_CONST function.
+    If type is FUNC_ITEM, then we have a fudged item_func_neg()
+    on our hands and return the underlying type.
     For Item_func_set_collation()
     e.g. NAME_CONST('name', 'value' COLLATE collation) we return its
     'value' argument type. 
   */
-  if (!valid_args)
-    return NULL_ITEM;
   Item::Type value_type= value_item->type();
   if (value_type == FUNC_ITEM)
   {

sql/item.h

@@ -820,6 +820,10 @@ protected:
     return tmp_table_field_from_field_type(table);
   }
   Field *create_tmp_field_int(TABLE *table, uint convert_int_length);
+  Field *tmp_table_field_from_field_type_maybe_null(TABLE *table,
+                                            Tmp_field_src *src,
+                                            const Tmp_field_param *param,
+                                            bool is_explicit_null);
 
   void push_note_converted_to_negative_complement(THD *thd);
   void push_note_converted_to_positive_complement(THD *thd);
@@ -876,6 +880,7 @@ public:
     expressions with subqueries in the ORDER/GROUP clauses.
   */
   String *val_str() { return val_str(&str_value); }
+  virtual Item_func *get_item_func() { return NULL; }
 
   const MY_LOCALE *locale_from_val_str();
 
@@ -2574,7 +2579,20 @@ protected:
   Item_basic_value(THD *thd): Item(thd) {}
 public:
   Field *create_tmp_field_ex(TABLE *table, Tmp_field_src *src,
-                             const Tmp_field_param *param);
+                             const Tmp_field_param *param)
+  {
+
+    /*
+      create_tmp_field_ex() for this type of Items is called for:
+      - CREATE TABLE ... SELECT
+      - In ORDER BY: SELECT max(a) FROM t1 GROUP BY a ORDER BY 'const';
+      - In CURSORS:
+          DECLARE c CURSOR FOR SELECT 'test';
+          OPEN c;
+    */
+    return tmp_table_field_from_field_type_maybe_null(table, src, param,
+                                            type() == Item::NULL_ITEM);
+  }
   bool eq(const Item *item, bool binary_cmp) const;
   const Type_all_attributes *get_type_all_attributes_from_const() const
   { return this; }
@@ -2915,7 +2933,6 @@ class Item_name_const : public Item_fixed_hybrid
 {
   Item *value_item;
   Item *name_item;
-  bool valid_args;
 public:
   Item_name_const(THD *thd, Item *name_arg, Item *val);
 
@@ -2948,7 +2965,8 @@ public:
         DECLARE c CURSOR FOR SELECT NAME_CONST('x','y') FROM t1;
         OPEN c;
     */
-    return create_tmp_field_ex_simple(table, src, param);
+    return tmp_table_field_from_field_type_maybe_null(table, src, param,
+                                              type() == Item::NULL_ITEM);
   }
   int save_in_field(Field *field, bool no_conversions)
   {

sql/item_cmpfunc.h

@@ -3313,11 +3313,8 @@ public:
 
 inline bool is_cond_and(Item *item)
 {
-  if (item->type() != Item::COND_ITEM)
-    return FALSE;
-
-  Item_cond *cond_item= (Item_cond*) item;
-  return (cond_item->functype() == Item_func::COND_AND_FUNC);
+  Item_func *func_item= item->get_item_func();
+  return func_item && func_item->functype() == Item_func::COND_AND_FUNC;
 }
 
 class Item_cond_or :public Item_cond
@@ -3418,11 +3415,8 @@ public:
 
 inline bool is_cond_or(Item *item)
 {
-  if (item->type() != Item::COND_ITEM)
-    return FALSE;
-
-  Item_cond *cond_item= (Item_cond*) item;
-  return (cond_item->functype() == Item_func::COND_OR_FUNC);
+  Item_func *func_item= item->get_item_func();
+  return func_item && func_item->functype() == Item_func::COND_OR_FUNC;
 }
 
 Item *and_expressions(Item *a, Item *b, Item **org_item);

sql/item_func.h

@@ -393,6 +393,7 @@ public:
 
   bool with_sum_func() const { return m_with_sum_func; }
   With_sum_func_cache* get_with_sum_func_cache() { return this; }
+  Item_func *get_item_func() { return this; }
 };
 
 

sql/sql_select.cc

@@ -16616,6 +16616,22 @@ Field *Item::create_tmp_field_int(TABLE *table, uint convert_int_length)
                                       *this, table);
 }
 
+Field *Item::tmp_table_field_from_field_type_maybe_null(TABLE *table,
+                                            Tmp_field_src *src,
+                                            const Tmp_field_param *param,
+                                            bool is_explicit_null)
+{
+  DBUG_ASSERT(!param->make_copy_field());
+  DBUG_ASSERT(!is_result_field());
+  Field *result;
+  if ((result= tmp_table_field_from_field_type(table)))
+  {
+    if (result && is_explicit_null)
+      result->is_created_from_null_item= true;
+  }
+  return result;
+}
+
 
 Field *Item_sum::create_tmp_field(bool group, TABLE *table)
 {
@@ -16847,31 +16863,6 @@ Field *Item_func_sp::create_tmp_field_ex(TABLE *table,
   return result;
 }
 
-
-Field *Item_basic_value::create_tmp_field_ex(TABLE *table,
-                                             Tmp_field_src *src,
-                                             const Tmp_field_param *param)
-{
-  /*
-    create_tmp_field_ex() for this type of Items is called for:
-    - CREATE TABLE ... SELECT
-    - In ORDER BY: SELECT max(a) FROM t1 GROUP BY a ORDER BY 'const';
-    - In CURSORS:
-        DECLARE c CURSOR FOR SELECT 'test';
-        OPEN c;
-  */
-  DBUG_ASSERT(!param->make_copy_field());
-  DBUG_ASSERT(!is_result_field());
-  Field *result;
-  if ((result= tmp_table_field_from_field_type(table)))
-  {
-    if (type() == Item::NULL_ITEM) // Item_null or Item_param
-      result->is_created_from_null_item= true;
-  }
-  return result;
-}
-
-
 /**
   Create field for temporary table.