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NAME

ALTER DOMAIN - 改变一个域的定义

SYNOPSIS

ALTER DOMAIN name
    { SET DEFAULT expression | DROP DEFAULT }
ALTER DOMAIN name
    { SET | DROP } NOT NULL
ALTER DOMAIN name
    ADD domain_constraint
ALTER DOMAIN name
    DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ]
ALTER DOMAIN name
    OWNER TO new_owner

DESCRIPTION 描述

ALTER DOMAIN 修改一个现有域的定义。它有几种子形式：

SET/DROP DEFAULT: 这些形式设置或者删除一个域的缺省值。请注意缺省只适用于随后的 INSERT 命令；他们并不影响使用该域已经在表中的行。
SET/DROP NOT NULL: 这些形式改变一个域是否标记为允许 NULL 值或者是拒绝 NULL 值。在使用域的字段包含非空的值的时候，你只可以 SET NOT NULL。
ADD domain_constraint: 这种形式向域中增加一种新的约束，使用的语法和 CREATE DOMAIN [create_domain(7)] 一样。这样做只有在所有使用域的字段满足新的约束的条件下才能成功。
DROP CONSTRAINT: 这种形式删除一个域上的约束。
OWNER: 这种形式把域的所有者改变为另外一个用户。

要使用 ALTER DOMAIN，你必须拥有该域；但是使用 ALTER DOMAIN OWNER 的时候你必须是数据库超级用户。

PARAMETERS 参数

name: 一个要修改的现有域的名字（可以有模式修饰）。
domain_constraint: 域的新的域约束。
constraint_name: 要删除的现有约束。
CASCADE: 自动删除依赖这个对象的约束。
RESTRICT: 如果有任何依赖对象，则拒绝删除约束。这是缺省行为。
new_owner: 域的新所有者的用户名。

EXAMPLES 例子

给一个域增加一个 NOT NULL 约束：

ALTER DOMAIN zipcode SET NOT NULL;

从一个域里删除一个 NOT NULL 约束：

ALTER DOMAIN zipcode DROP NOT NULL;

给一个域里增加一个检查约束：

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

从一个域里删除一个检查约束：

ALTER DOMAIN zipcode DROP CONSTRAINT zipchk;

#p#

NAME

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
ALTER DOMAIN name
    DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ]
ALTER DOMAIN name
    OWNER TO new_owner

DESCRIPTION

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 may only SET NOT NULL when the columns using the domain contain no null values.
ADD domain_constraint: This form adds a new constraint to a domain using the same syntax as CREATE DOMAIN [create_domain(7)]. This will only succeed if all columns using the domain satisfy the new constraint.
DROP CONSTRAINT: This form drops constraints on a domain.
OWNER: This form changes the owner of the domain to the specified user.

You must own the domain to use ALTER DOMAIN; except for ALTER DOMAIN OWNER, which may only be executed by a superuser.

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.
CASCADE: Automatically drop objects that depend on the constraint.
RESTRICT: Refuse to drop the constraint if there are any dependent objects. This is the default behavior.
new_owner: The user name of the new owner of the domain.

EXAMPLES

To add a NOT NULL constraint to a domain:

ALTER DOMAIN zipcode SET NOT NULL;

To remove a NOT NULL constraint from a domain:

ALTER DOMAIN zipcode DROP NOT NULL;

To add a check constraint to a domain:

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

To remove a check constraint from a domain:

ALTER DOMAIN zipcode DROP CONSTRAINT zipchk;