MDEV-13916 Enforce check constraint on JSON type

When creating a field of type JSON, it will be automatically
converted to TEXT with CHECK (json_valid(`a`)), if there wasn't any
previous check for the column.

Additional things:
- Added two bug fixes that was found while testing JSON. These bug
  fixes has also been pushed to 10.3 (with a test case), but as they
  where minimal and needed to get this task done and tested, the fixes
  are repeated here.
  - CREATE TABLE ... SELECT drops constraints for columns that
    are both in the create and select part.
  - If one has both a default expression and check constraint for a
    column, one can get the error "Expression for field `a` is refering
    to uninitialized field `a`.
- Removed some duplicate MYSQL_PLUGIN_IMPORT symbols

1 files changed, 10 insertions, 5 deletions

diff --git a/sql/sql_type.h b/sql/sql_type.h
index 3eb7d39742c..d507241075e 100644
--- a/sql/sql_type.h
+++ b/sql/sql_type.h
@@ -3280,6 +3280,7 @@ public:
     return true;
   }
   virtual bool is_scalar_type() const { return true; }
+  virtual bool is_json_type() const { return false; }
   virtual bool can_return_int() const { return true; }
   virtual bool can_return_decimal() const { return true; }
   virtual bool can_return_real() const { return true; }
@@ -5890,6 +5891,14 @@ public:
 };
 
 
+class Type_handler_json: public Type_handler_long_blob
+{
+public:
+  virtual ~Type_handler_json() {}
+  virtual bool is_json_type() const { return true; }
+};
+
+
 class Type_handler_blob: public Type_handler_blob_common
 {
   static const Name m_name_blob;
@@ -6218,6 +6227,7 @@ extern MYSQL_PLUGIN_IMPORT Type_handler_hex_hybrid  type_handler_hex_hybrid;
 extern MYSQL_PLUGIN_IMPORT Type_handler_tiny_blob   type_handler_tiny_blob;
 extern MYSQL_PLUGIN_IMPORT Type_handler_medium_blob type_handler_medium_blob;
 extern MYSQL_PLUGIN_IMPORT Type_handler_long_blob   type_handler_long_blob;
+extern MYSQL_PLUGIN_IMPORT Type_handler_json        type_handler_json;
 extern MYSQL_PLUGIN_IMPORT Type_handler_blob        type_handler_blob;
 
 extern MYSQL_PLUGIN_IMPORT Type_handler_bool        type_handler_bool;
@@ -6243,11 +6253,6 @@ extern MYSQL_PLUGIN_IMPORT Type_handler_datetime2   type_handler_datetime2;
 extern MYSQL_PLUGIN_IMPORT Type_handler_timestamp   type_handler_timestamp;
 extern MYSQL_PLUGIN_IMPORT Type_handler_timestamp2  type_handler_timestamp2;
 
-extern MYSQL_PLUGIN_IMPORT Type_handler_tiny_blob   type_handler_tiny_blob;
-extern MYSQL_PLUGIN_IMPORT Type_handler_blob        type_handler_blob;
-extern MYSQL_PLUGIN_IMPORT Type_handler_medium_blob type_handler_medium_blob;
-extern MYSQL_PLUGIN_IMPORT Type_handler_long_blob   type_handler_long_blob;
-
 extern MYSQL_PLUGIN_IMPORT Type_handler_interval_DDhhmmssff
   type_handler_interval_DDhhmmssff;