Postgresql 中文操作指南

ALTER DOMAIN

ALTER DOMAIN—更改域的定义

ALTER DOMAIN — change the definition of a domain

Synopsis

ALTER DOMAIN name
    { SET DEFAULT expression | DROP DEFAULT }
ALTER DOMAIN name
    { SET | DROP } NOT NULL
ALTER DOMAIN name
    ADD domain_constraint [ NOT VALID ]
ALTER DOMAIN name
    DROP CONSTRAINT [ IF EXISTS ] constraint_name [ RESTRICT | CASCADE ]
ALTER DOMAIN name
     RENAME CONSTRAINT constraint_name TO new_constraint_name
ALTER DOMAIN name
    VALIDATE CONSTRAINT constraint_name
ALTER DOMAIN name
    OWNER TO { new_owner | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
ALTER DOMAIN name
    RENAME TO new_name
ALTER DOMAIN name
    SET SCHEMA new_schema

Description

ALTER DOMAIN 更改现有域的定义。有几种子格式：

ALTER DOMAIN changes the definition of an existing domain. There are several sub-forms:

  • SET/DROP DEFAULT

    • These forms set or remove the default value for a domain. Note that defaults only apply to subsequent INSERT commands; they do not affect rows already in a table using the domain.

  • SET/DROP NOT NULL

    • These forms change whether a domain is marked to allow NULL values or to reject NULL values. You can only SET NOT NULL when the columns using the domain contain no null values.

  • ADD _domain_constraint [ NOT VALID ]_

    • This form adds a new constraint to a domain using the same syntax as CREATE DOMAIN. When a new constraint is added to a domain, all columns using that domain will be checked against the newly added constraint. These checks can be suppressed by adding the new constraint using the NOT VALID option; the constraint can later be made valid using ALTER DOMAIN …​ VALIDATE CONSTRAINT. Newly inserted or updated rows are always checked against all constraints, even those marked NOT VALID. NOT VALID is only accepted for CHECK constraints.

  • DROP CONSTRAINT [ IF EXISTS ]

    • This form drops constraints on a domain. If IF EXISTS is specified and the constraint does not exist, no error is thrown. In this case a notice is issued instead.

  • RENAME CONSTRAINT

    • This form changes the name of a constraint on a domain.

  • VALIDATE CONSTRAINT

    • This form validates a constraint previously added as NOT VALID, that is, it verifies that all values in table columns of the domain type satisfy the specified constraint.

  • OWNER

    • This form changes the owner of the domain to the specified user.

  • RENAME

    • This form changes the name of the domain.

  • SET SCHEMA

    • This form changes the schema of the domain. Any constraints associated with the domain are moved into the new schema as well.

您必须拥有该域才能使用 ALTER DOMAIN 。若要更改域的架构，您还必须在新架构上具有 CREATE 权限。若要变更所有者，您必须能够 SET ROLE 至新的拥有角色，并且该角色必须对该域的架构具有 CREATE 权限。（这些限制实施了对域的所有者所做的变更并不会通过删除和重新创建该域而执行任何操作。然而，超级使用者即便如此也可以变更任何域的所有权。）

You must own the domain to use ALTER DOMAIN. To change the schema of a domain, 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 domain’s schema. (These restrictions enforce that altering the owner doesn’t do anything you couldn’t do by dropping and recreating the domain. However, a superuser can alter ownership of any domain anyway.)

Parameters

  • name

    • The name (possibly schema-qualified) of an existing domain to alter.

  • domain_constraint

    • New domain constraint for the domain.

  • constraint_name

    • Name of an existing constraint to drop or rename.

  • NOT VALID

    • Do not verify existing stored data for constraint validity.

  • CASCADE

    • Automatically drop objects that depend on the constraint, and in turn all objects that depend on those objects (see Section 5.14).

  • RESTRICT

    • Refuse to drop the constraint if there are any dependent objects. This is the default behavior.

  • new_name

    • The new name for the domain.

  • new_constraint_name

    • The new name for the constraint.

  • new_owner

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

  • new_schema

    • The new schema for the domain.

Notes

虽然 ALTER DOMAIN ADD CONSTRAINT 尝试验证现有存储数据是否满足新约束，但此检查并非万无一失，这是因为该命令无法“看到”新插入或更新但尚未提交的表行。如果存在并发操作可能会插入无效数据，则应该采取以下方法进行：使用 NOT VALID 选项添加该约束，提交该命令，等到在那次提交之前启动的所有事务都完成，然后发出 ALTER DOMAIN VALIDATE CONSTRAINT 以搜索违反该约束的数据。该方法很可靠，这是因为一旦提交该约束，就可以保证所有新事务都针对该域类型的任何新值强制执行此约束。

Although ALTER DOMAIN ADD CONSTRAINT attempts to verify that existing stored data satisfies the new constraint, this check is not bulletproof, because the command cannot “see” table rows that are newly inserted or updated and not yet committed. If there is a hazard that concurrent operations might insert bad data, the way to proceed is to add the constraint using the NOT VALID option, commit that command, wait until all transactions started before that commit have finished, and then issue ALTER DOMAIN VALIDATE CONSTRAINT to search for data violating the constraint. This method is reliable because once the constraint is committed, all new transactions are guaranteed to enforce it against new values of the domain type.

当前，如果指定域或任何衍生域在数据库的任何表内用作容器类型的列（复合列、数组列或范围列）中，则 ALTER DOMAIN ADD CONSTRAINT 、 ALTER DOMAIN VALIDATE CONSTRAINT 和 ALTER DOMAIN SET NOT NULL 将会失败。最终应该对其加以改进，以针对此类嵌套值验证新约束。

Currently, ALTER DOMAIN ADD CONSTRAINT, ALTER DOMAIN VALIDATE CONSTRAINT, and ALTER DOMAIN SET NOT NULL will fail if the named domain or any derived domain is used within a container-type column (a composite, array, or range column) in any table in the database. They should eventually be improved to be able to verify the new constraint for such nested values.

Examples

若要向域中添加 NOT NULL 约束：

To add a NOT NULL constraint to a domain:

ALTER DOMAIN zipcode SET NOT NULL;

若要从域中移除 NOT NULL 约束：

To remove a NOT NULL constraint from a domain:

ALTER DOMAIN zipcode DROP NOT NULL;

如果要在域中添加检查约束：

To add a check constraint to a domain:

ALTER DOMAIN zipcode ADD CONSTRAINT zipchk CHECK (char_length(VALUE) = 5);

如果要在域中从检查约束中删除：

To remove a check constraint from a domain:

ALTER DOMAIN zipcode DROP CONSTRAINT zipchk;

如果要在域上重命名检查约束：

To rename a check constraint on a domain:

ALTER DOMAIN zipcode RENAME CONSTRAINT zipchk TO zip_check;

如果要将域移动到其他架构：

To move the domain into a different schema:

ALTER DOMAIN zipcode SET SCHEMA customers;

Compatibility

ALTER DOMAIN 遵循 SQL 标准，只除外 OWNER 、 RENAME 、 SET SCHEMA 和 VALIDATE CONSTRAINT 变体，它们是 PostgreSQL 扩展。 ADD CONSTRAINT 变体的 NOT VALID 子句也是 PostgreSQL 扩展。

ALTER DOMAIN conforms to the SQL standard, except for the OWNER, RENAME, SET SCHEMA, and VALIDATE CONSTRAINT variants, which are PostgreSQL extensions. The NOT VALID clause of the ADD CONSTRAINT variant is also a PostgreSQL extension.

See Also

CREATE DOMAIN , DROP DOMAIN

CREATE DOMAIN, DROP DOMAIN