Support dumping sequences

[kennytm]

Support dumping MariaDB and TiDB sequences. The sequence schema file should contain two statements:

CREATE SEQUENCE `seq_name` ...;
DO setval(`seq_name`, 1001);

The sequence value can be obtained by:

• MariaDB: SELECT next_not_cached_value FROM seq_name (a sequence is just a table in MariaDB)
• TiDB: no SQL statements yet, to be done.

[lichunzhu]

TiDB's show table next_row_id handle can get next_not_cached_value can get next_not_cached_value now.

mysql> show create sequence s;
+----------+--------------------------------------------------------------------------------------------------------------------------+
| Sequence | Create Sequence                                                                                                          |
+----------+--------------------------------------------------------------------------------------------------------------------------+
| s        | CREATE SEQUENCE `s` start with 1 minvalue 1 maxvalue 9223372036854775806 increment by 1 cache 1000 nocycle ENGINE=InnoDB |
+----------+--------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show table test.s next_row_id;
+---------+------------+-------------+--------------------+----------------+
| DB_NAME | TABLE_NAME | COLUMN_NAME | NEXT_GLOBAL_ROW_ID | ID_TYPE        |
+---------+------------+-------------+--------------------+----------------+
| test    | s          | _tidb_rowid |                  1 | AUTO_INCREMENT |
| test    | s          |             |                  1 | SEQUENCE       |
+---------+------------+-------------+--------------------+----------------+
2 rows in set (0.00 sec)

mysql> select nextval(s);
+------------+
| nextval(s) |
+------------+
|          1 |
+------------+
1 row in set (0.01 sec)

mysql> show table test.s next_row_id;
+---------+------------+-------------+--------------------+----------------+
| DB_NAME | TABLE_NAME | COLUMN_NAME | NEXT_GLOBAL_ROW_ID | ID_TYPE        |
+---------+------------+-------------+--------------------+----------------+
| test    | s          | _tidb_rowid |                  1 | AUTO_INCREMENT |
| test    | s          |             |               1001 | SEQUENCE       |
+---------+------------+-------------+--------------------+----------------+
2 rows in set (0.00 sec)

Dumpling should support using show create sequence to get sequence SQL and use select setval(seq, next_not_cached_value) to rebase sequence start value to next_not_cached_value. Both SQLs should be written in format like test.s-schema-sequence.

[lichunzhu]

sql example:
test-s-schema-sequence.sql

CREATE SEQUENCE `s` start with 1 minvalue 1 maxvalue 9223372036854775806 increment by 1 cache 1000 nocycle ENGINE=InnoDB;
select setval(s, 1001);