MDEV-16888 Add virtual Type_handler::cond_notnull_field_isnull_to_field_eq_zero()

sql/item_cmpfunc.h

@@ -2518,9 +2518,8 @@ class Item_func_isnull :public Item_func_null_predicate
     {
       Field *field=((Item_field*) args[0]->real_item())->field;
 
-      if (((field->type() == MYSQL_TYPE_DATE) ||
-          (field->type() == MYSQL_TYPE_DATETIME)) &&
-          (field->flags & NOT_NULL_FLAG))
+      if ((field->flags & NOT_NULL_FLAG) &&
+          field->type_handler()->cond_notnull_field_isnull_to_field_eq_zero())
         return true;
     }
     return false;

sql/sql_select.cc

@@ -16360,9 +16360,8 @@ Item_func_isnull::remove_eq_conds(THD *thd, Item::cond_result *cond_value,
   {
     Field *field= ((Item_field*) real_item)->field;
 
-    if (((field->type() == MYSQL_TYPE_DATE) ||
-         (field->type() == MYSQL_TYPE_DATETIME)) &&
-         (field->flags & NOT_NULL_FLAG))
+    if ((field->flags & NOT_NULL_FLAG) &&
+        field->type_handler()->cond_notnull_field_isnull_to_field_eq_zero())
     {
       /* fix to replace 'NULL' dates with '0' (shreeve@uci.edu) */
       /*

sql/sql_type.h

@@ -1399,6 +1399,17 @@ class Type_handler
   {
     return false;
   }
+  /*
+    Returns true if this data type supports a hack that
+      WHERE notnull_column IS NULL
+    finds zero values, e.g.:
+      WHERE date_notnull_column IS NULL        ->
+      WHERE date_notnull_column = '0000-00-00'
+  */
+  virtual bool cond_notnull_field_isnull_to_field_eq_zero() const
+  {
+    return false;
+  }
   /**
     Check whether a field type can be partially indexed by a key.
     @param  type   field type
@@ -3344,6 +3355,10 @@ class Type_handler_date_common: public Type_handler_temporal_with_date
   {
     return MYSQL_TIMESTAMP_DATE;
   }
+  bool cond_notnull_field_isnull_to_field_eq_zero() const
+  {
+    return true;
+  }
   Item_literal *create_literal_item(THD *thd, const char *str, size_t length,
                                     CHARSET_INFO *cs, bool send_error) const;
   Item *create_typecast_item(THD *thd, Item *item,
@@ -3425,6 +3440,10 @@ class Type_handler_datetime_common: public Type_handler_temporal_with_date
   {
     return MYSQL_TIMESTAMP_DATETIME;
   }
+  bool cond_notnull_field_isnull_to_field_eq_zero() const
+  {
+    return true;
+  }
   Item *create_typecast_item(THD *thd, Item *item,
                              const Type_cast_attributes &attr) const;
   void Column_definition_implicit_upgrade(Column_definition *c) const;