MDEV-31618: Server crashes in process_i_s_table_temporary_tables/get_all_tables

- Pre-open temporary table on sequence creation.
- Without this patch, if rename alter is done on the temporary sequence,
  and after that `create replace`, since table is not preopened and
  alter rename marked the table as reopen, and such table is deleted in
  the `find_temporary_table()` leaving the share without the table, that
  causes `show tables` to fail
- Closes PR #2685
- Reviewer: <serg@mariadb.com>

mysql-test/main/information_schema_temp_table.result

@@ -231,3 +231,38 @@ def	test	t1	BASE TABLE	MyISAM	10	Fixed	1	7	X	X	X	X	NULL	X	X	NULL	latin1_swedish_
 def	test	t2	TEMPORARY	MRG_MyISAM	10	Fixed	0	0	X	X	X	X	NULL	X	X	NULL	latin1_swedish_ci	NULL			X	Y
 def	test	t3	BASE TABLE	MRG_MyISAM	10	Fixed	1	5	X	X	X	X	NULL	X	X	NULL	latin1_swedish_ci	NULL			X	N
 DROP TABLE t1,t2,t3;
+#
+# MDEV-31618: Server crashes in
+#             process_i_s_table_temporary_tables/get_all_tables
+#
+CREATE TEMPORARY SEQUENCE seq1;
+SHOW FULL TABLES;
+Tables_in_test	Table_type
+seq1	TEMPORARY SEQUENCE
+SELECT table_schema, table_name FROM  INFORMATION_SCHEMA.TABLES WHERE table_type='temporary sequence';
+table_schema	table_name
+test	seq1
+mysqltest	s2
+mysqltest	s1
+ALTER TABLE `seq1` CHANGE `cache_size` cache_size int;
+ERROR HY000: Sequence 'test.seq1' table structure is invalid (cache_size)
+SHOW FULL TABLES;
+Tables_in_test	Table_type
+seq1	TEMPORARY SEQUENCE
+SELECT table_schema, table_name FROM  INFORMATION_SCHEMA.TABLES WHERE table_type='temporary sequence';
+table_schema	table_name
+test	seq1
+mysqltest	s2
+mysqltest	s1
+CREATE OR REPLACE TEMPORARY SEQUENCE seq1;
+SHOW FULL TABLES;
+Tables_in_test	Table_type
+seq1	TEMPORARY SEQUENCE
+SELECT table_schema, table_name FROM  INFORMATION_SCHEMA.TABLES WHERE table_type='temporary sequence';
+table_schema	table_name
+test	seq1
+mysqltest	s2
+mysqltest	s1
+DROP TABLE seq1;
+DROP TABLE mysqltest.s1;
+DROP TABLE mysqltest.s2;

mysql-test/main/information_schema_temp_table.test

@@ -219,3 +219,26 @@ CREATE TABLE t3 (a INT) ENGINE=MERGE UNION=(t1);
 --replace_column 10 X 11 X 12 X 13 X 15 X 16 X 22 X
 SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'test';
 DROP TABLE t1,t2,t3;
+
+--echo #
+--echo # MDEV-31618: Server crashes in
+--echo #             process_i_s_table_temporary_tables/get_all_tables
+--echo #
+
+CREATE TEMPORARY SEQUENCE seq1;
+# Check show temp tables before alter
+SHOW FULL TABLES;
+SELECT table_schema, table_name FROM  INFORMATION_SCHEMA.TABLES WHERE table_type='temporary sequence';
+--error 4086
+ALTER TABLE `seq1` CHANGE `cache_size` cache_size int;
+# Check show temp tables after alter
+SHOW FULL TABLES;
+SELECT table_schema, table_name FROM  INFORMATION_SCHEMA.TABLES WHERE table_type='temporary sequence';
+
+CREATE OR REPLACE TEMPORARY SEQUENCE seq1;
+# Check show temp tables after create/replace alter
+SHOW FULL TABLES;
+SELECT table_schema, table_name FROM  INFORMATION_SCHEMA.TABLES WHERE table_type='temporary sequence';
+DROP TABLE seq1;
+DROP TABLE mysqltest.s1;
+DROP TABLE mysqltest.s2;

sql/sql_parse.cc

@@ -787,6 +787,7 @@ void init_update_queries(void)
     Note that SQLCOM_RENAME_TABLE should not be in this list!
   */
   sql_command_flags[SQLCOM_CREATE_TABLE]|=    CF_PREOPEN_TMP_TABLES;
+  sql_command_flags[SQLCOM_CREATE_SEQUENCE]|= CF_PREOPEN_TMP_TABLES;
   sql_command_flags[SQLCOM_CREATE_INDEX]|=    CF_PREOPEN_TMP_TABLES;
   sql_command_flags[SQLCOM_ALTER_TABLE]|=     CF_PREOPEN_TMP_TABLES;
   sql_command_flags[SQLCOM_TRUNCATE]|=        CF_PREOPEN_TMP_TABLES;

sql/sql_show.cc

@@ -5351,7 +5351,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
                                  system_charset_info);
         schema_table_store_record(thd, table);
       }
-      else /* SCH_TABLE */
+      else /* SCH_TABLES */
         process_i_s_table_temporary_tables(thd, table, tmp_tbl);
     }
   }