MDEV-3873 & MDEV-3876 & MDEV-3912 : Wrong result (extra rows) with ALL subquery

from a MERGE view.

The problem was in the lost ability to be null for the table of a left join if it
is a view/derived table.

It hapenned because setup_table_map(), was called earlier then we merged
the view or derived.

Fixed by propagating new maybe_null flag during Item::update_used_tables().

Change in join_outer.test and join_outer_jcl6.test appeared because
IS NULL reported no used tables (i.e. constant) for argument which could not be
NULL and new maybe_null flag was propagated for IS NULL argument (Item_field)
because table the Item_field belonged to changed its maybe_null status.

14 files changed, 175 insertions, 120 deletions

diff --git a/sql/item.cc b/sql/item.cc
index 16dbd011f22..aee35b611e7 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -9166,11 +9166,18 @@ table_map Item_ref::used_tables() const
 
 
 void Item_ref::update_used_tables() 
-{ 
+{
   if (!get_depended_from())
-    (*ref)->update_used_tables(); 
+    (*ref)->update_used_tables();
+  maybe_null= (*ref)->maybe_null;
 }
 
+void Item_direct_view_ref::update_used_tables()
+{
+  Item_ref::update_used_tables();
+  if (view->table && view->table->maybe_null)
+    maybe_null= TRUE;
+}
 
 table_map Item_direct_view_ref::used_tables() const
 {
diff --git a/sql/item.h b/sql/item.h
index 0852287cc7f..2b5e867feb7 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -1849,9 +1849,14 @@ public:
         bitmap_fast_test_and_set(tab->read_set, field->field_index);
       if (field->vcol_info)
         tab->mark_virtual_col(field);
-    }  
+    }
+  }
+  void update_used_tables()
+  {
+    update_table_bitmaps();
+    if (field && field->table)
+      maybe_null= field->maybe_null();
   }
-  void update_used_tables() { update_table_bitmaps(); }
   Item *get_tmp_table_item(THD *thd);
   bool collect_item_field_processor(uchar * arg);
   bool add_field_to_set_processor(uchar * arg);
@@ -2874,7 +2879,11 @@ public:
   enum Item_result result_type () const { return orig_item->result_type(); }
   enum_field_types field_type() const   { return orig_item->field_type(); }
   table_map used_tables() const { return orig_item->used_tables(); }
-  void update_used_tables() { orig_item->update_used_tables(); }
+  void update_used_tables()
+  {
+    orig_item->update_used_tables();
+    maybe_null= orig_item->maybe_null;
+  }
   bool const_item() const { return orig_item->const_item(); }
   table_map not_null_tables() const { return orig_item->not_null_tables(); }
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg)
@@ -2966,6 +2975,7 @@ public:
   Item *replace_equal_field(uchar *arg);
   table_map used_tables() const;	
   table_map not_null_tables() const;
+  void update_used_tables();
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg)
   { 
     return (*ref)->walk(processor, walk_subquery, arg) ||
diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index b3b20a55ed9..75d3f31d4cd 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -1351,7 +1351,7 @@ int Arg_comparator::compare_e_row()
 
 void Item_func_truth::fix_length_and_dec()
 {
-  maybe_null= 0;
+  set_persist_maybe_null(0);
   null_value= 0;
   decimals= 0;
   max_length= 1;
@@ -1859,7 +1859,8 @@ longlong Item_func_eq::val_int()
 void Item_func_equal::fix_length_and_dec()
 {
   Item_bool_func2::fix_length_and_dec();
-  maybe_null=null_value=0;
+  set_persist_maybe_null(0);
+  null_value= 0;
 }
 
 longlong Item_func_equal::val_int()
@@ -1999,7 +2000,7 @@ void Item_func_interval::fix_length_and_dec()
       }
     }
   }
-  maybe_null= 0;
+  set_persist_maybe_null(0);
   max_length= 2;
   used_tables_cache|= row->used_tables();
   not_null_tables_cache= row->not_null_tables();
@@ -2670,7 +2671,7 @@ void
 Item_func_nullif::fix_length_and_dec()
 {
   Item_bool_func2::fix_length_and_dec();
-  maybe_null=1;
+  set_persist_maybe_null(1);
   if (args[0])					// Only false if EOM
   {
     max_length=args[0]->max_length;
@@ -4465,6 +4466,8 @@ void Item_cond::update_used_tables()
     item->update_used_tables();
     used_tables_cache|= item->used_tables();
     const_item_cache&= item->const_item();
+    if (!persistent_maybe_null && item->maybe_null)
+      maybe_null= 1;
   }
 }
 
@@ -4639,10 +4642,9 @@ longlong Item_is_not_null_test::val_int()
 */
 void Item_is_not_null_test::update_used_tables()
 {
+  args[0]->update_used_tables();
   if (!args[0]->maybe_null)
     used_tables_cache= 0;			/* is always true */
-  else
-    args[0]->update_used_tables();
 }
 
 
@@ -4925,7 +4927,7 @@ Item_func_regex::fix_fields(THD *thd, Item **ref)
     int comp_res= regcomp(TRUE);
     if (comp_res == -1)
     {						// Will always return NULL
-      maybe_null=1;
+      set_persist_maybe_null(1);
       fixed= 1;
       return FALSE;
     }
@@ -4935,7 +4937,7 @@ Item_func_regex::fix_fields(THD *thd, Item **ref)
     maybe_null= args[0]->maybe_null;
   }
   else
-    maybe_null=1;
+    set_persist_maybe_null(1);
   fixed= 1;
   return FALSE;
 }
@@ -5729,6 +5731,8 @@ void Item_equal::update_used_tables()
     item->update_used_tables();
     used_tables_cache|= item->used_tables();
     const_item_cache&= item->const_item();
+    if (!persistent_maybe_null && item->maybe_null)
+      maybe_null= 1;
   }
 }
 
diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index 143fef87abd..dca139e6321 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -757,6 +757,11 @@ public:
   my_decimal *decimal_op(my_decimal *);
   enum_field_types field_type() const;
   void fix_length_and_dec();
+  void update_used_tables()
+  {
+    Item_func_coalesce::update_used_tables();
+    maybe_null= args[1]->maybe_null;
+  }
   const char *func_name() const { return "ifnull"; }
   Field *tmp_table_field(TABLE *table);
   uint decimal_precision() const;
@@ -779,6 +784,11 @@ public:
   enum_field_types field_type() const { return cached_field_type; }
   bool fix_fields(THD *, Item **);
   void fix_length_and_dec();
+  void update_used_tables()
+  {
+    Item_func::update_used_tables();
+    maybe_null= args[1]->maybe_null || args[2]->maybe_null;
+  }
   uint decimal_precision() const;
   const char *func_name() const { return "if"; }
   bool eval_not_null_tables(uchar *opt_arg);
@@ -1242,6 +1252,12 @@ public:
   my_decimal *val_decimal(my_decimal *);
   bool fix_fields(THD *thd, Item **ref);
   void fix_length_and_dec();
+  void update_used_tables()
+  {
+    Item_func::update_used_tables();
+    if (else_expr_num == -1 || args[else_expr_num]->maybe_null)
+      maybe_null= 1;
+  }
   uint decimal_precision() const;
   table_map not_null_tables() const { return 0; }
   enum Item_result result_type () const { return cached_result_type; }
@@ -1363,13 +1379,14 @@ public:
   enum Functype functype() const { return ISNULL_FUNC; }
   void fix_length_and_dec()
   {
-    decimals=0; max_length=1; maybe_null=0;
+    decimals=0; max_length=1; set_persist_maybe_null(0);
     update_used_tables();
   }
   const char *func_name() const { return "isnull"; }
   /* Optimize case of not_null_column IS NULL */
   virtual void update_used_tables()
   {
+    args[0]->update_used_tables();
     if (!args[0]->maybe_null)
     {
       used_tables_cache= 0;			/* is always false */
@@ -1377,7 +1394,6 @@ public:
     }
     else
     {
-      args[0]->update_used_tables();
       used_tables_cache= args[0]->used_tables();
       const_item_cache= args[0]->const_item();
     }
@@ -1424,7 +1440,7 @@ public:
   enum Functype functype() const { return ISNOTNULL_FUNC; }
   void fix_length_and_dec()
   {
-    decimals=0; max_length=1; maybe_null=0;
+    decimals=0; max_length=1; set_persist_maybe_null(0);
   }
   const char *func_name() const { return "isnotnull"; }
   optimize_type select_optimize() const { return OPTIMIZE_NULL; }
@@ -1495,6 +1511,12 @@ public:
   void cleanup();
   longlong val_int();
   bool fix_fields(THD *thd, Item **ref);
+  void update_used_tables()
+  {
+    Item_bool_func::update_used_tables();
+    if (regex_is_const)
+      maybe_null= 1;
+  }
   const char *func_name() const { return "regexp"; }
 
   virtual inline void print(String *str, enum_query_type query_type)
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 42332d6b1b2..0cd96619023 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -86,7 +86,7 @@ void Item_func::set_arguments(List<Item> &list)
 }
 
 Item_func::Item_func(List<Item> &list)
-  :allowed_arg_cols(1)
+  :allowed_arg_cols(1), persistent_maybe_null(0)
 {
   set_arguments(list);
 }
@@ -94,6 +94,7 @@ Item_func::Item_func(List<Item> &list)
 Item_func::Item_func(THD *thd, Item_func *item)
   :Item_result_field(thd, item),
    allowed_arg_cols(item->allowed_arg_cols),
+   persistent_maybe_null(0),
    arg_count(item->arg_count),
    used_tables_cache(item->used_tables_cache),
    not_null_tables_cache(item->not_null_tables_cache),
@@ -423,6 +424,8 @@ void Item_func::update_used_tables()
     args[i]->update_used_tables();
     used_tables_cache|=args[i]->used_tables();
     const_item_cache&=args[i]->const_item();
+    if (!persistent_maybe_null && args[i]->maybe_null)
+      maybe_null= 1;
   }
 }
 
@@ -1496,7 +1499,7 @@ void Item_func_div::fix_length_and_dec()
   case IMPOSSIBLE_RESULT:
     DBUG_ASSERT(0);
   }
-  maybe_null= 1; // devision by zero
+  set_persist_maybe_null(1); // devision by zero
   DBUG_VOID_RETURN;
 }
 
@@ -1531,7 +1534,7 @@ void Item_func_int_div::fix_length_and_dec()
   max_length=args[0]->max_length -
     (argtype == DECIMAL_RESULT || argtype == INT_RESULT ?
      args[0]->decimals : 0);
-  maybe_null=1;
+  set_persist_maybe_null(1);
   unsigned_flag=args[0]->unsigned_flag | args[1]->unsigned_flag;
 }
 
@@ -1612,7 +1615,7 @@ void Item_func_mod::result_precision()
 void Item_func_mod::fix_length_and_dec()
 {
   Item_num_op::fix_length_and_dec();
-  maybe_null= 1;
+  set_persist_maybe_null(1);
   unsigned_flag= args[0]->unsigned_flag;
 }
 
@@ -2778,7 +2781,7 @@ longlong Item_func_field::val_int()
 
 void Item_func_field::fix_length_and_dec()
 {
-  maybe_null=0; max_length=3;
+  set_persist_maybe_null(0); max_length=3;
   cmp_type= args[0]->result_type();
   for (uint i=1; i < arg_count ; i++)
     cmp_type= item_cmp_type(cmp_type, args[i]->result_type());
@@ -4843,7 +4846,7 @@ void Item_func_get_user_var::fix_length_and_dec()
 {
   THD *thd=current_thd;
   int error;
-  maybe_null=1;
+  set_persist_maybe_null(1);
   decimals=NOT_FIXED_DEC;
   max_length=MAX_BLOB_WIDTH;
 
@@ -5049,7 +5052,7 @@ void Item_func_get_system_var::update_null_value()
 void Item_func_get_system_var::fix_length_and_dec()
 {
   char *cptr;
-  maybe_null= TRUE;
+  set_persist_maybe_null(1);
   max_length= 0;
 
   if (var->check_type(var_type))
@@ -5580,7 +5583,7 @@ bool Item_func_match::fix_fields(THD *thd, Item **ref)
   DBUG_ASSERT(fixed == 0);
   Item *UNINIT_VAR(item);                        // Safe as arg_count is > 1
 
-  maybe_null=1;
+  set_persist_maybe_null(1);
   join_key=0;
 
   /*
@@ -5914,7 +5917,7 @@ longlong Item_func_row_count::val_int()
 Item_func_sp::Item_func_sp(Name_resolution_context *context_arg, sp_name *name)
   :Item_func(), context(context_arg), m_name(name), m_sp(NULL), sp_result_field(NULL)
 {
-  maybe_null= 1;
+  set_persist_maybe_null(1);
   m_name->init_qname(current_thd);
   dummy_table= (TABLE*) sql_calloc(sizeof(TABLE)+ sizeof(TABLE_SHARE));
   dummy_table->s= (TABLE_SHARE*) (dummy_table+1);
@@ -5925,7 +5928,7 @@ Item_func_sp::Item_func_sp(Name_resolution_context *context_arg,
                            sp_name *name, List<Item> &list)
   :Item_func(list), context(context_arg), m_name(name), m_sp(NULL),sp_result_field(NULL)
 {
-  maybe_null= 1;
+  set_persist_maybe_null(1);
   m_name->init_qname(current_thd);
   dummy_table= (TABLE*) sql_calloc(sizeof(TABLE)+ sizeof(TABLE_SHARE));
   dummy_table->s= (TABLE_SHARE*) (dummy_table+1);
@@ -6066,7 +6069,7 @@ void Item_func_sp::fix_length_and_dec()
   decimals= sp_result_field->decimals();
   max_length= sp_result_field->field_length;
   collation.set(sp_result_field->charset());
-  maybe_null= 1;
+  set_persist_maybe_null(1);
   unsigned_flag= test(sp_result_field->flags & UNSIGNED_FLAG);
 
   DBUG_VOID_RETURN;
diff --git a/sql/item_func.h b/sql/item_func.h
index 082c9b83296..3ab1fbad4e3 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -38,6 +38,8 @@ protected:
     0 means get this number from first argument
   */
   uint allowed_arg_cols;
+  /* maybe_null can't be changed by parameters or used table state */
+  bool persistent_maybe_null;
 public:
   uint arg_count;
   table_map used_tables_cache, not_null_tables_cache;
@@ -63,13 +65,13 @@ public:
   enum Type type() const { return FUNC_ITEM; }
   virtual enum Functype functype() const   { return UNKNOWN_FUNC; }
   Item_func(void):
-    allowed_arg_cols(1), arg_count(0)
+    allowed_arg_cols(1), persistent_maybe_null(0), arg_count(0)
   {
     with_sum_func= 0;
     with_field= 0;
   }
   Item_func(Item *a):
-    allowed_arg_cols(1), arg_count(1)
+    allowed_arg_cols(1), persistent_maybe_null(0), arg_count(1)
   {
     args= tmp_arg;
     args[0]= a;
@@ -77,7 +79,7 @@ public:
     with_field= a->with_field;
   }
   Item_func(Item *a,Item *b):
-    allowed_arg_cols(1), arg_count(2)
+    allowed_arg_cols(1), persistent_maybe_null(0), arg_count(2)
   {
     args= tmp_arg;
     args[0]= a; args[1]= b;
@@ -85,7 +87,7 @@ public:
     with_field= a->with_field || b->with_field;
   }
   Item_func(Item *a,Item *b,Item *c):
-    allowed_arg_cols(1)
+    allowed_arg_cols(1), persistent_maybe_null(0)
   {
     arg_count= 0;
     if ((args= (Item**) sql_alloc(sizeof(Item*)*3)))
@@ -97,7 +99,7 @@ public:
     }
   }
   Item_func(Item *a,Item *b,Item *c,Item *d):
-    allowed_arg_cols(1)
+    allowed_arg_cols(1), persistent_maybe_null(0)
   {
     arg_count= 0;
     if ((args= (Item**) sql_alloc(sizeof(Item*)*4)))
@@ -111,7 +113,7 @@ public:
     }
   }
   Item_func(Item *a,Item *b,Item *c,Item *d,Item* e):
-    allowed_arg_cols(1)
+    allowed_arg_cols(1), persistent_maybe_null(0)
   {
     arg_count= 5;
     if ((args= (Item**) sql_alloc(sizeof(Item*)*5)))
@@ -300,6 +302,11 @@ public:
     info.bool_function= &Item::restore_to_before_no_rows_in_result;
     walk(&Item::call_bool_func_processor, FALSE, (uchar*) &info);
   }
+  inline void set_persist_maybe_null(bool mb_null)
+  {
+    maybe_null= mb_null;
+    persistent_maybe_null= 1;
+  }
 };
 
 
@@ -506,7 +513,7 @@ public:
   }
   double val_real();
   enum_field_types field_type() const { return MYSQL_TYPE_DOUBLE; }
-  void fix_length_and_dec() { maybe_null= 1; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); }
   const char *func_name() const { return "double_typecast"; }
   virtual void print(String *str, enum_query_type query_type);
 };
@@ -647,7 +654,7 @@ class Item_dec_func :public Item_real_func
   void fix_length_and_dec()
   {
     decimals=NOT_FIXED_DEC; max_length=float_length(decimals);
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
 };
 
@@ -971,7 +978,7 @@ public:
   Item_func_coercibility(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "coercibility"; }
-  void fix_length_and_dec() { max_length=10; maybe_null= 0; }
+  void fix_length_and_dec() { max_length=10; set_persist_maybe_null(0); }
   table_map not_null_tables() const { return 0; }
 };
 
@@ -1132,7 +1139,7 @@ public:
   {}
   longlong val_int();
   const char *func_name() const { return "benchmark"; }
-  void fix_length_and_dec() { max_length=1; maybe_null=0; }
+  void fix_length_and_dec() { max_length=1; set_persist_maybe_null(0); }
   virtual void print(String *str, enum_query_type query_type);
   bool check_vcol_func_processor(uchar *int_arg) 
   {
@@ -1385,7 +1392,7 @@ public:
   double val_real() { DBUG_ASSERT(fixed == 1); null_value= 1; return 0.0; }
   longlong val_int() { DBUG_ASSERT(fixed == 1); null_value=1; return 0; }
   enum Item_result result_type () const { return STRING_RESULT; }
-  void fix_length_and_dec() { maybe_null=1; max_length=0; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); max_length=0; }
 };
 
 #endif /* HAVE_DLOPEN */
@@ -1406,7 +1413,7 @@ class Item_func_get_lock :public Item_int_func
   Item_func_get_lock(Item *a,Item *b) :Item_int_func(a,b) {}
   longlong val_int();
   const char *func_name() const { return "get_lock"; }
-  void fix_length_and_dec() { max_length=1; maybe_null=1;}
+  void fix_length_and_dec() { max_length=1; set_persist_maybe_null(1);}
   bool check_vcol_func_processor(uchar *int_arg) 
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name());
@@ -1420,7 +1427,7 @@ public:
   Item_func_release_lock(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "release_lock"; }
-  void fix_length_and_dec() { max_length=1; maybe_null=1;}
+  void fix_length_and_dec() { max_length=1; set_persist_maybe_null(1);}
   bool check_vcol_func_processor(uchar *int_arg) 
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name());
@@ -1437,7 +1444,7 @@ public:
   Item_master_pos_wait(Item *a,Item *b,Item *c) :Item_int_func(a,b,c) {}
   longlong val_int();
   const char *func_name() const { return "master_pos_wait"; }
-  void fix_length_and_dec() { max_length=21; maybe_null=1;}
+  void fix_length_and_dec() { max_length=21; set_persist_maybe_null(1);}
   bool check_vcol_func_processor(uchar *int_arg) 
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name());
@@ -1653,7 +1660,8 @@ public:
   Item_func_inet_aton(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "inet_aton"; }
-  void fix_length_and_dec() { decimals= 0; max_length= 21; maybe_null= 1; unsigned_flag= 1;}
+  void fix_length_and_dec()
+  { decimals= 0; max_length= 21; set_persist_maybe_null(1); unsigned_flag= 1; }
 };
 
 
@@ -1722,7 +1730,8 @@ public:
   Item_func_is_free_lock(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "is_free_lock"; }
-  void fix_length_and_dec() { decimals=0; max_length=1; maybe_null=1;}
+  void fix_length_and_dec()
+  { decimals= 0; max_length= 1; set_persist_maybe_null(1); }
   bool check_vcol_func_processor(uchar *int_arg) 
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name());
@@ -1736,7 +1745,8 @@ public:
   Item_func_is_used_lock(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "is_used_lock"; }
-  void fix_length_and_dec() { decimals=0; max_length=10; maybe_null=1;}
+  void fix_length_and_dec()
+  { decimals= 0; max_length= 10; set_persist_maybe_null(1);}
   bool check_vcol_func_processor(uchar *int_arg) 
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name());
@@ -1759,7 +1769,7 @@ public:
   Item_func_row_count() :Item_int_func() {}
   longlong val_int();
   const char *func_name() const { return "row_count"; }
-  void fix_length_and_dec() { decimals= 0; maybe_null=0; }
+  void fix_length_and_dec() { decimals= 0; set_persist_maybe_null(0); }
   bool check_vcol_func_processor(uchar *int_arg) 
   {
 
@@ -1893,7 +1903,7 @@ public:
   Item_func_found_rows() :Item_int_func() {}
   longlong val_int();
   const char *func_name() const { return "found_rows"; }
-  void fix_length_and_dec() { decimals= 0; maybe_null=0; }
+  void fix_length_and_dec() { decimals= 0; set_persist_maybe_null(0); }
   bool check_vcol_func_processor(uchar *int_arg) 
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name());
diff --git a/sql/item_geofunc.cc b/sql/item_geofunc.cc
index 522be28558f..ba330ba3b96 100644
--- a/sql/item_geofunc.cc
+++ b/sql/item_geofunc.cc
@@ -52,7 +52,7 @@ void Item_geometry_func::fix_length_and_dec()
   collation.set(&my_charset_bin);
   decimals=0;
   max_length= (uint32) 4294967295U;
-  maybe_null= 1;
+  set_persist_maybe_null(1);
 }
 
 
@@ -145,7 +145,7 @@ void Item_func_as_wkt::fix_length_and_dec()
 {
   collation.set(default_charset(), DERIVATION_COERCIBLE, MY_REPERTOIRE_ASCII);
   max_length=MAX_BLOB_WIDTH;
-  maybe_null= 1;
+  set_persist_maybe_null(1);
 }
 
 
diff --git a/sql/item_geofunc.h b/sql/item_geofunc.h
index d2030ee7bb9..eae6f425f4d 100644
--- a/sql/item_geofunc.h
+++ b/sql/item_geofunc.h
@@ -89,7 +89,7 @@ public:
   {
     // "GeometryCollection" is the longest
     max_length= 20;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   };
 };
 
@@ -224,7 +224,7 @@ public:
   {
     Item_func::print(str, query_type);
   }
-  void fix_length_and_dec() { maybe_null= 1; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); }
   bool is_null() { (void) val_int(); return null_value; }
 };
 
@@ -251,7 +251,7 @@ public:
     Item_func::print(str, query_type);
   }
 
-  void fix_length_and_dec() { maybe_null= 1; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); }
   bool is_null() { (void) val_int(); return null_value; }
 };
 
@@ -342,7 +342,7 @@ public:
   longlong val_int();
   optimize_type select_optimize() const { return OPTIMIZE_NONE; }
   const char *func_name() const { return "st_isempty"; }
-  void fix_length_and_dec() { maybe_null= 1; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); }
 };
 
 class Item_func_issimple: public Item_bool_func
@@ -356,7 +356,7 @@ public:
   longlong val_int();
   optimize_type select_optimize() const { return OPTIMIZE_NONE; }
   const char *func_name() const { return "st_issimple"; }
-  void fix_length_and_dec() { maybe_null= 1; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); }
 };
 
 class Item_func_isclosed: public Item_bool_func
@@ -366,7 +366,7 @@ public:
   longlong val_int();
   optimize_type select_optimize() const { return OPTIMIZE_NONE; }
   const char *func_name() const { return "st_isclosed"; }
-  void fix_length_and_dec() { maybe_null= 1; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); }
 };
 
 class Item_func_dimension: public Item_int_func
@@ -376,7 +376,7 @@ public:
   Item_func_dimension(Item *a): Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "st_dimension"; }
-  void fix_length_and_dec() { max_length= 10; maybe_null= 1; }
+  void fix_length_and_dec() { max_length= 10; set_persist_maybe_null(1); }
 };
 
 class Item_func_x: public Item_real_func
@@ -389,7 +389,7 @@ public:
   void fix_length_and_dec() 
   { 
     Item_real_func::fix_length_and_dec();
-    maybe_null= 1; 
+    set_persist_maybe_null(1);
   }
 };
 
@@ -404,7 +404,7 @@ public:
   void fix_length_and_dec() 
   { 
     Item_real_func::fix_length_and_dec();
-    maybe_null= 1; 
+    set_persist_maybe_null(1);
   }
 };
 
@@ -416,7 +416,7 @@ public:
   Item_func_numgeometries(Item *a): Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "st_numgeometries"; }
-  void fix_length_and_dec() { max_length= 10; maybe_null= 1; }
+  void fix_length_and_dec() { max_length= 10; set_persist_maybe_null(1); }
 };
 
 
@@ -427,7 +427,7 @@ public:
   Item_func_numinteriorring(Item *a): Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "st_numinteriorrings"; }
-  void fix_length_and_dec() { max_length= 10; maybe_null= 1; }
+  void fix_length_and_dec() { max_length= 10; set_persist_maybe_null(1); }
 };
 
 
@@ -438,7 +438,7 @@ public:
   Item_func_numpoints(Item *a): Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "st_numpoints"; }
-  void fix_length_and_dec() { max_length= 10; maybe_null= 1; }
+  void fix_length_and_dec() { max_length= 10; set_persist_maybe_null(1); }
 };
 
 
@@ -452,7 +452,7 @@ public:
   void fix_length_and_dec() 
   { 
     Item_real_func::fix_length_and_dec();
-    maybe_null= 1; 
+    set_persist_maybe_null(1);
   }
 };
 
@@ -467,7 +467,7 @@ public:
   void fix_length_and_dec() 
   { 
     Item_real_func::fix_length_and_dec();
-    maybe_null= 1; 
+    set_persist_maybe_null(1);
   }
 };
 
@@ -479,7 +479,7 @@ public:
   Item_func_srid(Item *a): Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "srid"; }
-  void fix_length_and_dec() { max_length= 10; maybe_null= 1; }
+  void fix_length_and_dec() { max_length= 10; set_persist_maybe_null(1); }
 };
 
 
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 1b228a344f4..d0b284a363d 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -272,7 +272,7 @@ String *Item_func_aes_decrypt::val_str(String *str)
 void Item_func_aes_decrypt::fix_length_and_dec()
 {
    max_length=args[0]->max_length;
-   maybe_null= 1;
+   set_persist_maybe_null(1);
 }
 
 
@@ -435,7 +435,7 @@ void Item_func_concat::fix_length_and_dec()
   if (max_result_length >= MAX_BLOB_WIDTH)
   {
     max_result_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
   max_length= (ulong) max_result_length;
 }
@@ -795,7 +795,7 @@ void Item_func_concat_ws::fix_length_and_dec()
   if (max_result_length >= MAX_BLOB_WIDTH)
   {
     max_result_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
   max_length= (ulong) max_result_length;
 }
@@ -997,7 +997,7 @@ void Item_func_replace::fix_length_and_dec()
   if (max_result_length >= MAX_BLOB_WIDTH)
   {
     max_result_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
   max_length= (ulong) max_result_length;
   
@@ -1081,7 +1081,7 @@ void Item_func_insert::fix_length_and_dec()
   if (max_result_length >= MAX_BLOB_WIDTH)
   {
     max_result_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
   max_length= (ulong) max_result_length;
 }
@@ -2184,7 +2184,7 @@ void Item_func_elt::fix_length_and_dec()
     set_if_bigger(max_length,args[i]->max_length);
     set_if_bigger(decimals,args[i]->decimals);
   }
-  maybe_null=1;					// NULL if wrong first arg
+  set_persist_maybe_null(1);			  // NULL if wrong first arg
 }
 
 
@@ -2419,14 +2419,14 @@ void Item_func_repeat::fix_length_and_dec()
     if (max_result_length >= MAX_BLOB_WIDTH)
     {
       max_result_length= MAX_BLOB_WIDTH;
-      maybe_null= 1;
+      set_persist_maybe_null(1);
     }
     max_length= (ulong) max_result_length;
   }
   else
   {
     max_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
 }
 
@@ -2509,14 +2509,14 @@ void Item_func_rpad::fix_length_and_dec()
     if (length >= MAX_BLOB_WIDTH)
     {
       length= MAX_BLOB_WIDTH;
-      maybe_null= 1;
+      set_persist_maybe_null(1);
     }
     max_length= (ulong) length;
   }
   else
   {
     max_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
 }
 
@@ -2626,14 +2626,14 @@ void Item_func_lpad::fix_length_and_dec()
     if (length >= MAX_BLOB_WIDTH)
     {
       length= MAX_BLOB_WIDTH;
-      maybe_null= 1;
+      set_persist_maybe_null(1);
     }
     max_length= (ulong) length;
   }
   else
   {
     max_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
 }
 
@@ -3548,7 +3548,7 @@ bool Item_func_dyncol_create::fix_fields(THD *thd, Item **ref)
 
 void Item_func_dyncol_create::fix_length_and_dec()
 {
-  maybe_null= TRUE;
+  set_persist_maybe_null(1);
   collation.set(&my_charset_bin);
   decimals= 0;
 }
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index fc4e888e6ea..e3b040a2e55 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -319,7 +319,7 @@ public:
   String *val_str(String *);
   void fix_length_and_dec()
   {
-    maybe_null=1;
+    set_persist_maybe_null(1);
     /* 9 = MAX ((8- (arg_len % 8)) + 1) */
     max_length = args[0]->max_length + 9;
   }
@@ -335,7 +335,7 @@ public:
   String *val_str(String *);
   void fix_length_and_dec()
   {
-    maybe_null=1;
+    set_persist_maybe_null(1);
     /* 9 = MAX ((8- (arg_len % 8)) + 1) */
     max_length = args[0]->max_length - 9;
   }
@@ -361,7 +361,7 @@ public:
     constructor_helper();
   }
   String *val_str(String *);
-  void fix_length_and_dec() { maybe_null=1; max_length = 13; }
+  void fix_length_and_dec() { set_persist_maybe_null(1); max_length = 13; }
   const char *func_name() const { return "encrypt"; }
   bool check_vcol_func_processor(uchar *int_arg) 
   {
@@ -431,7 +431,7 @@ public:
   void fix_length_and_dec()
   {
     max_length= MAX_FIELD_NAME * system_charset_info->mbmaxlen;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   const char *func_name() const { return "database"; }
   const char *fully_qualified_func_name() const { return "database()"; }
@@ -607,7 +607,7 @@ public:
   {
     collation.set(default_charset());
     max_length=64;
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
 };
 
@@ -634,7 +634,7 @@ public:
   Item_func_unhex(Item *a) :Item_str_func(a) 
   { 
     /* there can be bad hex strings */
-    maybe_null= 1; 
+    set_persist_maybe_null(1);
   }
   const char *func_name() const { return "unhex"; }
   String *val_str(String *);
@@ -680,7 +680,7 @@ public:
   void fix_length_and_dec()
   {
     collation.set(&my_charset_bin, DERIVATION_COERCIBLE);
-    maybe_null=1;
+    set_persist_maybe_null(1);
     max_length=MAX_BLOB_WIDTH;
   }
   bool check_vcol_func_processor(uchar *int_arg) 
@@ -713,7 +713,7 @@ public:
   { 
     decimals= 0; 
     max_length= 3 * 8 + 7; 
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
 };
 
@@ -804,7 +804,7 @@ public:
   {
      collation.set(system_charset_info);
      max_length= 64 * collation.collation->mbmaxlen; // should be enough
-     maybe_null= 0;
+     set_persist_maybe_null(0);
   };
   table_map not_null_tables() const { return 0; }
 };
@@ -819,7 +819,7 @@ public:
   {
      collation.set(system_charset_info);
      max_length= 64 * collation.collation->mbmaxlen; // should be enough
-     maybe_null= 0;
+     set_persist_maybe_null(0);
   };
   table_map not_null_tables() const { return 0; }
 };
@@ -865,7 +865,8 @@ class Item_func_uncompress: public Item_str_func
   String buffer;
 public:
   Item_func_uncompress(Item *a): Item_str_func(a){}
-  void fix_length_and_dec(){ maybe_null= 1; max_length= MAX_BLOB_WIDTH; }
+  void fix_length_and_dec()
+  { set_persist_maybe_null(1); max_length= MAX_BLOB_WIDTH; }
   const char *func_name() const{return "uncompress";}
   String *val_str(String *) ZLIB_DEPENDED_FUNCTION
 };
@@ -937,7 +938,7 @@ public:
     max_length= MAX_DYNAMIC_COLUMN_LENGTH;
   }
   void fix_length_and_dec()
-  { maybe_null= 1; }
+  { set_persist_maybe_null(1); }
   /* Mark that collation can change between calls */
   bool dynamic_result() { return 1; }
 
@@ -956,7 +957,8 @@ class Item_func_dyncol_list: public Item_str_func
 {
 public:
   Item_func_dyncol_list(Item *str) :Item_str_func(str) {};
-  void fix_length_and_dec() { maybe_null= 1; max_length= MAX_BLOB_WIDTH; };
+  void fix_length_and_dec()
+  { set_persist_maybe_null(1); max_length= MAX_BLOB_WIDTH; };
   const char *func_name() const{ return "column_list"; }
   String *val_str(String *);
 };
diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index bdad96f12ef..eaddd39fa58 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -877,7 +877,7 @@ void Item_func_monthname::fix_length_and_dec()
   collation.set(cs, DERIVATION_COERCIBLE, repertoire);
   decimals=0;
   max_length= locale->max_month_name_length * collation.collation->mbmaxlen;
-  maybe_null=1; 
+  set_persist_maybe_null(1);
 }
 
 
@@ -1030,7 +1030,7 @@ void Item_func_dayname::fix_length_and_dec()
   collation.set(cs, DERIVATION_COERCIBLE, repertoire);
   decimals=0;
   max_length= locale->max_day_name_length * collation.collation->mbmaxlen;
-  maybe_null=1; 
+  set_persist_maybe_null(1);
 }
 
 
@@ -1404,7 +1404,7 @@ void Item_func_curdate::fix_length_and_dec()
   ltime.hour= ltime.minute= ltime.second= 0;
   ltime.time_type= MYSQL_TIMESTAMP_DATE;
   Item_datefunc::fix_length_and_dec();
-  maybe_null= false;
+  set_persist_maybe_null(0);
 }
 
 /**
@@ -1643,7 +1643,7 @@ void Item_func_date_format::fix_length_and_dec()
                    collation.collation->mbmaxlen;
     set_if_smaller(max_length,MAX_BLOB_WIDTH);
   }
-  maybe_null=1;					// If wrong date
+  set_persist_maybe_null(1);				// If wrong date
 }
 
 
@@ -1992,7 +1992,7 @@ void Item_extract::print(String *str, enum_query_type query_type)
 
 void Item_extract::fix_length_and_dec()
 {
-  maybe_null=1;					// If wrong date
+  set_persist_maybe_null(1);					// If wrong date
   switch (int_type) {
   case INTERVAL_YEAR:		max_length=4; date_value=1; break;
   case INTERVAL_YEAR_MONTH:	max_length=6; date_value=1; break;
diff --git a/sql/item_timefunc.h b/sql/item_timefunc.h
index 8d19e59ddfb..25a160d91f6 100644
--- a/sql/item_timefunc.h
+++ b/sql/item_timefunc.h
@@ -67,7 +67,7 @@ public:
   { 
     decimals=0; 
     max_length=6*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1; 
+    set_persist_maybe_null(1);
   }
   enum_monotonicity_info get_monotonicity_info() const;
   longlong val_int_endpoint(bool left_endp, bool *incl_endp);
@@ -90,7 +90,7 @@ public:
   { 
     decimals=0; 
     max_length=2*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1; 
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -123,7 +123,7 @@ public:
     collation.set(&my_charset_bin);
     decimals=0;
     max_length=2*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1; 
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -158,7 +158,7 @@ public:
   { 
     decimals=0;
     max_length=3*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1; 
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -179,7 +179,7 @@ public:
   {
     decimals=0;
     max_length=2*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -200,7 +200,7 @@ public:
   {
     decimals=0;
     max_length=2*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -221,7 +221,7 @@ public:
   { 
      decimals=0;
      max_length=1*MY_CHARSET_BIN_MB_MAXLEN;
-     maybe_null=1;
+     set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -242,7 +242,7 @@ public:
   { 
     decimals=0;
     max_length=2*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -263,7 +263,7 @@ public:
   { 
     decimals=0;
     max_length=2*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
 };
 
@@ -277,7 +277,7 @@ public:
   { 
     decimals=0;
     max_length=6*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -300,7 +300,7 @@ public:
   { 
     decimals=0;
     max_length=4*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -335,7 +335,7 @@ public:
     collation.set(&my_charset_bin);
     decimals=0;
     max_length=1*MY_CHARSET_BIN_MB_MAXLEN;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -415,7 +415,7 @@ public:
   const char *func_name() const { return "time_to_sec"; }
   void fix_num_length_and_dec()
   {
-    maybe_null= true;
+    set_persist_maybe_null(1);
     Item_func_seconds_hybrid::fix_num_length_and_dec();
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
@@ -454,7 +454,7 @@ public:
     { MAX_DATETIME_WIDTH, MAX_DATETIME_WIDTH, MAX_DATE_WIDTH,
       MAX_DATETIME_WIDTH, MIN_TIME_WIDTH };
 
-    maybe_null= true;
+    set_persist_maybe_null(1);
     max_length= max_time_type_width[mysql_type_to_time_type(field_type())+2];
     if (decimals)
     {
@@ -470,7 +470,7 @@ public:
       We set maybe_null to 1 as default as any bad argument with date or
       time can get us to return NULL.
     */ 
-    maybe_null= 1;
+    set_persist_maybe_null(1);
   }
 };
 
@@ -507,7 +507,7 @@ public:
   {
     store_now_in_TIME(&ltime);
     Item_timefunc::fix_length_and_dec();
-    maybe_null= false;
+    set_persist_maybe_null(0);
   }
   bool get_date(MYSQL_TIME *res, uint fuzzy_date);
   /* 
@@ -589,7 +589,7 @@ public:
   {
     store_now_in_TIME(&ltime);
     Item_temporal_func::fix_length_and_dec();
-    maybe_null= false;
+    set_persist_maybe_null(0);
   }
   bool get_date(MYSQL_TIME *res, uint fuzzy_date);
   virtual void store_now_in_TIME(MYSQL_TIME *now_time)=0;
@@ -930,7 +930,7 @@ public:
   void fix_length_and_dec() 
   { 
     decimals=0;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   bool check_partition_func_processor(uchar *int_arg) {return FALSE;}
   bool check_vcol_func_processor(uchar *int_arg) { return FALSE;}
@@ -952,7 +952,7 @@ public:
   void fix_length_and_dec()
   {
     decimals=0;
-    maybe_null=1;
+    set_persist_maybe_null(1);
   }
   virtual void print(String *str, enum_query_type query_type);
 };
@@ -974,7 +974,7 @@ public:
   const char *func_name() const { return "get_format"; }
   void fix_length_and_dec()
   {
-    maybe_null= 1;
+    set_persist_maybe_null(1);
     decimals=0;
     max_length=17*MY_CHARSET_BIN_MB_MAXLEN;
   }
diff --git a/sql/item_xmlfunc.cc b/sql/item_xmlfunc.cc
index 57995b2b643..faf5f345171 100644
--- a/sql/item_xmlfunc.cc
+++ b/sql/item_xmlfunc.cc
@@ -2579,6 +2579,7 @@ void Item_xml_str_func::fix_length_and_dec()
   int rc;
 
   nodeset_func= 0;
+  set_persist_maybe_null(1);
 
   if (agg_arg_charsets(collation, args, arg_count, MY_COLL_CMP_CONV, 1))
     return;
diff --git a/sql/item_xmlfunc.h b/sql/item_xmlfunc.h
index ce33d161c79..be56a83349f 100644
--- a/sql/item_xmlfunc.h
+++ b/sql/item_xmlfunc.h
@@ -30,14 +30,10 @@ protected:
 public:
   Item_xml_str_func(Item *a, Item *b): 
     Item_str_func(a,b) 
-  {
-    maybe_null= TRUE;
-  }
+  {}
   Item_xml_str_func(Item *a, Item *b, Item *c): 
     Item_str_func(a,b,c) 
-  {
-    maybe_null= TRUE;
-  }
+  {}
   void fix_length_and_dec();
   String *parse_xml(String *raw_xml, String *parsed_xml_buf);
   bool check_vcol_func_processor(uchar *int_arg)