本文主要介绍如何对使用Sequence类型作为自增列的表信息以及相关Sequence类型进行查看。

SHOW CREATE TABLE

当表为拆分表或者广播表时,显示自增列Sequence的类型。

查看已创建的表语法如下:

SHOW CREATE TABLE <name>
说明
  • SHOW CREATE TABLE仅显示相关Sequence的类型,并不显示Sequence详细信息,如需查看,请使用SHOW SEQUENCES命令。
  • 关联了单元化Group Sequence的表并不显示单元数量和单元索引,因此不能将SHOW CREATE TABLE显示的DDL直接用于创建具备同样单元化Group Sequence能力的表。
  • 如果需要创建具备同样单元化能力的表,必须使用SHOW SEQUENCES查看单元数量和单元索引,然后参照CREATE TABLE的语法修改通过SHOW CREATE TABLE获取的建表DDL。

示例

示例一:建表时指定AUTO_INCREMENT,但没有指定Sequence类型关键字,则默认使用Group Sequence

请在命令行输入如下代码:

mysql> SHOW CREATE TABLE tab1;

返回结果如下:

+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                           |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tab1  | CREATE TABLE `tab1` (
`col1` bigint(20) NOT NULL AUTO_INCREMENT BY GROUP,
`col2` varchar(16) DEFAULT NULL,
PRIMARY KEY (`col1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`col1`) |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

示例二:建表时为AUTO_INCREMENT指定了单元数量和单元索引,使用单元化 Group Sequence,但SHOW CREATE TABLE时并不显示单元数量和单元索引,不能将此DDL用于创建具备同样单元化 Group Sequence能力的表。

请在命令行输入如下代码:

mysql> SHOW CREATE TABLE tab2;

返回结果如下:

+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                           |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tab2  | CREATE TABLE `tab2` (
`col1` bigint(20) NOT NULL AUTO_INCREMENT BY GROUP,
`col2` varchar(16) DEFAULT NULL,
PRIMARY KEY (`col1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`col1`) |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

示例三:建表时为AUTO_INCREMENT指定了BY TIME,即Time-based Sequence类型。

请在命令行输入如下代码:

mysql> SHOW CREATE TABLE tab3;

返回结果如下:

+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                            |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tab3  | CREATE TABLE `tab3` (
`col1` bigint(20) NOT NULL AUTO_INCREMENT BY TIME,
`col2` varchar(16) DEFAULT NULL,
PRIMARY KEY (`col1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`col1`) |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

示例四:建表时为AUTO_INCREMENT指定了BY SIMPLE,即Simple Sequence类型。

请在命令行输入如下代码:

mysql> SHOW CREATE TABLE tab4;

返回结果如下:

+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                            |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tab3  | CREATE TABLE `tab4` (
`col1` bigint(20) NOT NULL AUTO_INCREMENT BY TIME,
`col2` varchar(16) DEFAULT NULL,
PRIMARY KEY (`col1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`col1`) |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

SHOW SEQUENCES

建表后相关的Sequence名称和详细信息,可通过SHOW SEQUENCES查看。

请在命令行输入如下代码:

mysql> SHOW SEQUENCES;

返回结果如下:

+---------------+--------+------------+------------+------------+--------------+------------+---------------------+-------+--------+
| NAME          | VALUE  | UNIT_COUNT | UNIT_INDEX | INNER_STEP | INCREMENT_BY | START_WITH | MAX_VALUE           | CYCLE | TYPE   |
+---------------+--------+------------+------------+------------+--------------+------------+---------------------+-------+--------+
| seq1          | 100000 | 1          | 0          | 100000     | N/A          | N/A        | N/A                 | N/A   | GROUP  |
| seq2          | 400000 | 3          | 1          | 100000     | N/A          | N/A        | N/A                 | N/A   | GROUP  |
| seq3          | N/A    | N/A        | N/A        | N/A        | N/A          | N/A        | N/A                 | N/A   | TIME   |
| seq4          | 1006   | N/A        | N/A        | N/A        | 2            | 1000       | 99999999999         | N     | SIMPLE |
| AUTO_SEQ_tab1 | 100000 | 1          | 0          | 100000     | N/A          | N/A        | N/A                 | N/A   | GROUP  |
| AUTO_SEQ_tab2 | 400000 | 3          | 1          | 100000     | N/A          | N/A        | N/A                 | N/A   | GROUP  |
| AUTO_SEQ_tab3 | N/A    | N/A        | N/A        | N/A        | N/A          | N/A        | N/A                 | N/A   | TIME   |
| AUTO_SEQ_tab4 | 2      | N/A        | N/A        | N/A        | 1            | 1          | 9223372036854775807 | N     | SIMPLE |
+---------------+--------+------------+------------+------------+--------------+------------+---------------------+-------+--------+
8 rows in set (0.01 sec)