Postgresql 中文操作指南

ALTER SEQUENCE

ALTER SEQUENCE —— 更改序列生成器的定义

ALTER SEQUENCE — change the definition of a sequence generator

Synopsis

ALTER SEQUENCE [ IF EXISTS ] name
    [ AS data_type ]
    [ INCREMENT [ BY ] increment ]
    [ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
    [ START [ WITH ] start ]
    [ RESTART [ [ WITH ] restart ] ]
    [ CACHE cache ] [ [ NO ] CYCLE ]
    [ OWNED BY { table_name.column_name | NONE } ]
ALTER SEQUENCE [ IF EXISTS ] name SET { LOGGED | UNLOGGED }
ALTER SEQUENCE [ IF EXISTS ] name OWNER TO { new_owner | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
ALTER SEQUENCE [ IF EXISTS ] name RENAME TO new_name
ALTER SEQUENCE [ IF EXISTS ] name SET SCHEMA new_schema

Description

ALTER SEQUENCE 更改现有序列生成器的参数。在 ALTER SEQUENCE 命令中未专门设置的任何参数将保留其先前的设置。

ALTER SEQUENCE changes the parameters of an existing sequence generator. Any parameters not specifically set in the ALTER SEQUENCE command retain their prior settings.

您必须拥有该序列才能使用 ALTER SEQUENCE 。要更改序列的架构，您还必须在新架构上具有 CREATE 权限。要更改所有者，您必须能够 SET ROLE 到新的所有角色，并且该角色必须对序列架构具有 CREATE 权限。（这些限制执行了不执行任何可以通过删除和重新创建序列来执行的操作，以更改所有者。但是，超级用户无论如何都可以更改任何序列的所有权。）

You must own the sequence to use ALTER SEQUENCE. To change a sequence’s schema, you must also have CREATE privilege on the new schema. To alter the owner, you must be able to SET ROLE to the new owning role, and that role must have CREATE privilege on the sequence’s schema. (These restrictions enforce that altering the owner doesn’t do anything you couldn’t do by dropping and recreating the sequence. However, a superuser can alter ownership of any sequence anyway.)

Parameters

  • name

    • The name (optionally schema-qualified) of a sequence to be altered.

  • IF EXISTS

    • Do not throw an error if the sequence does not exist. A notice is issued in this case.

  • data_type

    • The optional clause AS _data_type_ changes the data type of the sequence. Valid types are smallint, integer, and bigint.

    • Changing the data type automatically changes the minimum and maximum values of the sequence if and only if the previous minimum and maximum values were the minimum or maximum value of the old data type (in other words, if the sequence had been created using NO MINVALUE or NO MAXVALUE, implicitly or explicitly). Otherwise, the minimum and maximum values are preserved, unless new values are given as part of the same command. If the minimum and maximum values do not fit into the new data type, an error will be generated.

  • increment

    • The clause INCREMENT BY _increment_ is optional. A positive value will make an ascending sequence, a negative one a descending sequence. If unspecified, the old increment value will be maintained.

  • minvalue__NO MINVALUE

    • The optional clause MINVALUE _minvalue_ determines the minimum value a sequence can generate. If NO MINVALUE is specified, the defaults of 1 and the minimum value of the data type for ascending and descending sequences, respectively, will be used. If neither option is specified, the current minimum value will be maintained.

  • maxvalue__NO MAXVALUE

    • The optional clause MAXVALUE _maxvalue_ determines the maximum value for the sequence. If NO MAXVALUE is specified, the defaults of the maximum value of the data type and -1 for ascending and descending sequences, respectively, will be used. If neither option is specified, the current maximum value will be maintained.

  • start

    • The optional clause START WITH _start_ changes the recorded start value of the sequence. This has no effect on the current sequence value; it simply sets the value that future ALTER SEQUENCE RESTART commands will use.

  • restart

    • The optional clause RESTART [ WITH _restart ]_ changes the current value of the sequence. This is similar to calling the setval function with is_called = false: the specified value will be returned by the next call of nextval. Writing RESTART with no restart value is equivalent to supplying the start value that was recorded by CREATE SEQUENCE or last set by ALTER SEQUENCE START WITH.

    • In contrast to a setval call, a RESTART operation on a sequence is transactional and blocks concurrent transactions from obtaining numbers from the same sequence. If that’s not the desired mode of operation, setval should be used.

  • cache

    • The clause CACHE _cache_ enables sequence numbers to be preallocated and stored in memory for faster access. The minimum value is 1 (only one value can be generated at a time, i.e., no cache). If unspecified, the old cache value will be maintained.

  • CYCLE

    • The optional CYCLE key word can be used to enable the sequence to wrap around when the maxvalue or minvalue has been reached by an ascending or descending sequence respectively. If the limit is reached, the next number generated will be the minvalue or maxvalue, respectively.

  • NO CYCLE

    • If the optional NO CYCLE key word is specified, any calls to nextval after the sequence has reached its maximum value will return an error. If neither CYCLE or NO CYCLE are specified, the old cycle behavior will be maintained.

  • SET { LOGGED | UNLOGGED }

    • This form changes the sequence from unlogged to logged or vice-versa (see CREATE SEQUENCE). It cannot be applied to a temporary sequence.

  • OWNED BY table_name.column_name__OWNED BY NONE

    • The OWNED BY option causes the sequence to be associated with a specific table column, such that if that column (or its whole table) is dropped, the sequence will be automatically dropped as well. If specified, this association replaces any previously specified association for the sequence. The specified table must have the same owner and be in the same schema as the sequence. Specifying OWNED BY NONE removes any existing association, making the sequence “free-standing”.

  • new_owner

    • The user name of the new owner of the sequence.

  • new_name

    • The new name for the sequence.

  • new_schema

    • The new schema for the sequence.

Notes

ALTER SEQUENCE 不会立即影响 nextval 在除当前后端之外的已预分配（缓存）序列值的后台中的结果。在注意到已更改的序列生成参数之前，它们将使用所有缓存的值。当前后端将立即受到影响。

ALTER SEQUENCE will not immediately affect nextval results in backends, other than the current one, that have preallocated (cached) sequence values. They will use up all cached values prior to noticing the changed sequence generation parameters. The current backend will be affected immediately.

ALTER SEQUENCE 不会影响序列的 currval 状态。（在 PostgreSQL 8.3 之前，有时会这样做。）

ALTER SEQUENCE does not affect the currval status for the sequence. (Before PostgreSQL 8.3, it sometimes did.)

ALTER SEQUENCE 阻止并发 nextval 、 currval 、 lastval 和 setval 调用。

ALTER SEQUENCE blocks concurrent nextval, currval, lastval, and setval calls.

出于历史原因， ALTER TABLE 也可与序列一起使用；但是，与序列一起允许的 ALTER TABLE 唯一变体等效于上面显示的形式。

For historical reasons, ALTER TABLE can be used with sequences too; but the only variants of ALTER TABLE that are allowed with sequences are equivalent to the forms shown above.

Examples

以 105 重启一个名为 serial 的序列：

Restart a sequence called serial, at 105:

ALTER SEQUENCE serial RESTART WITH 105;

Compatibility

ALTER SEQUENCE 符合 SQL 标准，除了 AS 、 START WITH 、 OWNED BY 、 OWNER TO 、 RENAME TO 和 SET SCHEMA 子句，这些子句是 PostgreSQL 扩展。

ALTER SEQUENCE conforms to the SQL standard, except for the AS, START WITH, OWNED BY, OWNER TO, RENAME TO, and SET SCHEMA clauses, which are PostgreSQL extensions.

See Also

CREATE SEQUENCE 、 DROP SEQUENCE

CREATE SEQUENCE, DROP SEQUENCE