为啥修改不了数据类型

为什么修改不了数据类型啊
我创建了一个表，但是ponum 定义的长度太短，想给他改长点，用以以下语句，可一直提示错误
ALTER TABLE purchase_order4 ALTER COLUMN ponum CHARACTER(10);

CREATE TABLE purchase_order4
(
ponum character(5) NOT NULL,
qty character(10),
orderdate date,
duedate date,
receiveddate date,
CONSTRAINT purchase_order4_pkey PRIMARY KEY (ponum)
)
[解决办法]

--查询约束
sp_helpconstraint purchase_order4
--删除约束
ALTER TABLE purchase_order4 
drop constraint purchase_order4_pkey

然后你再修改下字段试试..
[解决办法]

ALTER TABLE purchase_order4  add constraint purchase_order4_pkey PRIMARY KEY(ponum)

还有别忘了再加回约束..
[解决办法]

CREATE TABLE purchase_order4

(
ponum character(5) NOT NULL,
qty character(10),
orderdate datetime,
duedate datetime,
receiveddate datetime,
CONSTRAINT purchase_order4_pkey PRIMARY KEY (ponum)
)
--改变前字符长度为5
/*
Column_name Type Computed Length Prec Scale Nullable TrimTrailingBlanks FixedLenNullInSource Collation
-------------------------------------------------------- -------------------------------------------------------- ----------------------------------- ----------- ----- ----- ----------------------------------- ----------------------------------- ----------------------------------- --------------------------------------------------------

ponum char no 5 no no no Chinese_PRC_CI_AS
qty char no 10 yes no yes Chinese_PRC_CI_AS

orderdate datetime no 8 yes (n/a) (n/a) NULL
duedate datetime no 8 yes (n/a) (n/a) NULL

receiveddate datetime no 8 yes (n/a) (n/a) NULL

*/
alter table purchase_order4
drop constraint purchase_order4_pkey
go
alter table purchase_order4
alter column ponum character(10) not null
go
alter table purchase_order4
add constraint purchase_order4_pkey primary key clustered (ponum)
--改变后字符长度为10
/*
Column_name Type Computed Length Prec Scale Nullable TrimTrailingBlanks FixedLenNullInSource Collation

-------------------------------------------------------- -------------------------------------------------------- ----------------------------------- ----------- ----- ----- ----------------------------------- ----------------------------------- ----------------------------------- --------------------------------------------------------
ponum char no 10 no no no Chinese_PRC_CI_AS
qty char no 10 yes no yes Chinese_PRC_CI_AS

orderdate datetime no 8 yes (n/a) (n/a) NULL
duedate datetime no 8 yes (n/a) (n/a) NULL

receiveddate datetime
*/

[解决办法]
先取消主键约束再修改，修改完再创建主键约束，不过我比较感兴趣你报什么错？
[解决办法]
需要更改的列有约束，需要先取消约束，再进行更改

ALTER TABLE purchase_order4 DROP CONSTRAINT purchase_order4_pkey
GO
ALTER TABLE purchase_order4 ALTER COLUMN ponum character(10) not null
GO
ALTER TABLE purchase_order4  ADD CONSTRAINT purchase_order4_pkey PRIMARY KEY( ponum )

[解决办法]
去掉约束，修改，在添加约束。
[解决办法]
有主键约束了，要先删除再修改。或者有权限，直接GUI界面修改。
[解决办法]
个人觉得和约束没关系，原因可能是原字段中中已有数据了
[解决办法]
说出你报的错误
[解决办法]
我试了只要在 character前加type 就可以了我用的是postgresql

为啥修改不了数据类型

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