MariaDB 10.3 序列
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在MariaDB 10.3版本中sequence是特殊的表,和表使用相同的namespace,因此表和序列的名字不能相同。 MariaDB [wuhan]> select version(); +--------------------+ | version() | +--------------------+ | 10.3.8-MariaDB-log | +--------------------+ 1 row in set (0.000 sec) MariaDB [wuhan]> create sequence s; Query OK, 0 rows affected (0.477 sec) MariaDB [wuhan]> show create sequence s; +-------+--------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+--------------------------------------------------------------------------------------------------------------------------+ | s | CREATE SEQUENCE `s` start with 1 minvalue 1 maxvalue 9223372036854775806 increment by 1 cache 1000 nocycle ENGINE=InnoDB | +-------+--------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.075 sec) MariaDB [wuhan]> show create table s\G *************************** 1. row *************************** Table: s Create Table: CREATE TABLE `s` ( `next_not_cached_value` bigint(21) NOT NULL, `minimum_value` bigint(21) NOT NULL, `maximum_value` bigint(21) NOT NULL, `start_value` bigint(21) NOT NULL COMMENT ‘start value when sequences is created or value if RESTART is used‘, `increment` bigint(21) NOT NULL COMMENT ‘increment value‘, `cache_size` bigint(21) unsigned NOT NULL, `cycle_option` tinyint(1) unsigned NOT NULL COMMENT ‘0 if no cycles are allowed, 1 if the sequence should begin a new cycle when maximum_value is passed‘, `cycle_count` bigint(21) NOT NULL COMMENT ‘How many cycles have been done‘ ) ENGINE=InnoDB SEQUENCE=1 1 row in set (0.000 sec) MariaDB [wuhan]> select * from s\G *************************** 1. row *************************** next_not_cached_value: 1 minimum_value: 1 maximum_value: 9223372036854775806 start_value: 1 increment: 1 cache_size: 1000 cycle_option: 0 cycle_count: 0 1 row in set (0.001 sec) cycle_count每次递增。 可以看到序列是一种特殊的表,对这种表不能update和delete,不能将表名和序列名命名为一样的,否则报错。 MariaDB [wuhan]> update s set increment=2 ; ERROR 1031 (HY000): Storage engine SEQUENCE of the table `wuhan`.`s` doesn‘t have this option MariaDB [wuhan]> delete from s where increment=1; ERROR 1031 (HY000): Storage engine SEQUENCE of the table `wuhan`.`s` doesn‘t have this option MariaDB [wuhan]> create table s(a int); ERROR 1050 (42S01): Table ‘s‘ already exists 但是对表的重命名、删除操作生效: MariaDB [wuhan]> alter table s rename to ss; Query OK, 0 rows affected (0.291 sec) MariaDB [wuhan]> rename table ss to s; Query OK, 0 rows affected (0.022 sec) MariaDB [wuhan]> drop table s; Query OK, 0 rows affected (0.076 sec) 对序列进行FLUSH TABLE操作将会关闭序列,生成的下一个序列值将会根据序列对象生成,实际上将会丢弃缓存cached 值。 MariaDB [wuhan]> create sequence s; Query OK, 0 rows affected (0.024 sec) MariaDB [wuhan]> select nextval(s),lastval(s); +------------+------------+ | nextval(s) | lastval(s) | +------------+------------+ | 1 | 1 | +------------+------------+ 1 row in set (0.059 sec) MariaDB [wuhan]> select nextval(s),lastval(s); +------------+------------+ | nextval(s) | lastval(s) | +------------+------------+ | 2 | 2 | +------------+------------+ 1 row in set (0.001 sec) MariaDB [wuhan]> flush table s; Query OK, 0 rows affected (0.001 sec) MariaDB [wuhan]> select nextval(s),lastval(s); +------------+------------+ | nextval(s) | lastval(s) | +------------+------------+ | 1001 | 1001 | +------------+------------+ 1 row in set (0.001 sec) MariaDB [wuhan]> flush table s; Query OK, 0 rows affected (0.000 sec) MariaDB [wuhan]> select nextval(s),lastval(s); +------------+------------+ | nextval(s) | lastval(s) | +------------+------------+ | 2001 | 2001 | +------------+------------+ 1 row in set (0.001 sec) 缺点: 由于在MariaDB中在很多应用场景中序列对象充当普通的表,将会受到lock table操作的影响。但是在其他DBMS中则不会受影响,比如oracle中的序列。 序列兼容性: MariaDB兼容ANSI SQL和oracle 序列的语法,oracle 语法的序列需要将SQL_MODE设置为SQL_MODE=oracle. 序列备份: 由于序列是只有一行数据的常规表,因此mysqldump可以很好的支持。 序列和复制: 若在master-master复制或者galera复制中使用序列,需要设置 INCREMENT=0,以告知sequence对象使用 auto_increment_increment和 auto_increment_offset对每个服务器产生唯一的序列值。
转自:
https://mariadb.com/kb/en/library/sequence-overview/
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