MDEV-32790: Output result in show create table for mysql_json type should be longtext

- We don't test `json` MySQL tables from `std_data` since the error `ER_TABLE_NEEDS_REBUILD
` is invoked. However MDEV-32235 will override this test after merge,
but leave it to show behavior and historical changes.

- Closes PR #2833
Reviewer: <cvicentiu@mariadb.org>
          <serg@mariadb.com>

mysql-test/main/mysql_json_table_recreate.result

@@ -169,3 +169,47 @@ Total_Number_of_Tests	Succesful_Tests	String_is_valid_JSON
 drop table tempty;
 drop table mysql_json_test;
 drop table mysql_json_test_big;
+#
+# MDEV-32790: Output result in show create table
+#             for mysql_json type should be longtext
+#
+create table t1(j json);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `j` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL CHECK (json_valid(`j`))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table t1;
+create table t1(j mysql_json);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `j` mysql_json /* JSON from MySQL 5.7 */ CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table t1;
+create table `testjson` (
+`t` json /* JSON from MySQL 5.7*/ CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL
+) ENGINE=InnoDB DEFAULT CH...' at line 2
+create table `testjson` (
+`t` json /* JSON from MySQL 5.7*/ COLLATE utf8mb4_bin NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;
+show create table testjson;
+Table	Create Table
+testjson	CREATE TABLE `testjson` (
+  `t` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL CHECK (json_valid(`t`))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table testjson;
+create table `testjson` (
+`t` longtext /* JSON from MySQL 5.7 */ CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;
+show create table testjson;
+Table	Create Table
+testjson	CREATE TABLE `testjson` (
+  `t` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table testjson;
+#
+# End of 10.5 tests
+#

mysql-test/main/mysql_json_table_recreate.test

@@ -88,3 +88,39 @@ from mysql_json_test_big;
 drop table tempty;
 drop table mysql_json_test;
 drop table mysql_json_test_big;
+
+--echo #
+--echo # MDEV-32790: Output result in show create table
+--echo #             for mysql_json type should be longtext
+--echo #
+
+create table t1(j json);
+show create table t1;
+drop table t1;
+create table t1(j mysql_json);
+show create table t1;
+drop table t1;
+# `json` type should not have character set and collation other than utf8mb4_bin
+--error ER_PARSE_ERROR
+create table `testjson` (
+  `t` json /* JSON from MySQL 5.7*/ CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;
+
+# By removing character set from `json` field query should work and
+# expand to `longtext` with characterset
+create table `testjson` (
+  `t` json /* JSON from MySQL 5.7*/ COLLATE utf8mb4_bin NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;
+show create table testjson;
+drop table testjson;
+
+# `longtext` that is alias can have character set
+create table `testjson` (
+  `t` longtext /* JSON from MySQL 5.7 */ CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci;
+show create table testjson;
+drop table testjson;
+
+--echo #
+--echo # End of 10.5 tests
+--echo #

plugin/type_mysql_json/type.cc

@@ -62,7 +62,7 @@ class Field_mysql_json: public Field_blob
   bool parse_mysql(String *dest, const char *data, size_t length) const;
   bool send(Protocol *protocol) { return Field::send(protocol); }
   void sql_type(String &s) const
-  { s.set_ascii(STRING_WITH_LEN("json /* MySQL 5.7 */")); }
+  { s.set_ascii(STRING_WITH_LEN("mysql_json /* JSON from MySQL 5.7 */")); }
   /* this will make ALTER TABLE to consider it different from built-in field */
   Compression_method *compression_method() const { return (Compression_method*)1; }
 };