Oracle中表列由VARCHAR2类型改成CLOB

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Oracle中表列由VARCHAR2类型改成CLOB

来源: 作者: 时间:2016-02-16 09:27 【

情景原来表中的列定义成VARCHAR2类型,众所周知,VARCHAR2类型最大支持长度为4000。如果由于业务需要,想把此列转换为CLOB类型,在Oracle中直接通过ALTER语句转换是行不通的。下面根据具体

情景

原来表中的列定义成VARCHAR2类型,众所周知,VARCHAR2类型最大支持长度为4000。如果由于业务需要,想把此列转换为CLOB类型,在Oracle中直接通过ALTER语句转换是行不通的。下面根据具体事例讲解在Oracle中如何把表列由VARCHAR2类型转换为CLOB类型。

示例准备

1. 新建两张张表TB_WITHOUT_DATA(此VARCHAR2列不包含数据)和TB_WITH_DATA(此Varchar2列包含数据)

create table TB_WITHOUT_DATA
(
  id NUMBER,
  name VARCHAR2(100),
  description VARCHAR2(2000)
);

 

create table TB_WITH_DATA
(
  id NUMBER,
  name VARCHAR2(100),
  description VARCHAR2(2000)
);

insert into TB_WITH_DATA VALUES (1,'David Louis','He is capable of resolving such kind of issue');
insert into TB_WITH_DATA VALUES (2,'German Noemi','She is very beatiful and charming');
insert into TB_WITH_DATA VALUES (3,'Oliver Queen','He is main actor in the Green Arrow');
insert into TB_WITH_DATA VALUES (4,'Mark Williams','He plays snooker very well');
insert into TB_WITH_DATA VALUES (5,'Sita Rama Raju Kata','I do not know this guy');
insert into TB_WITH_DATA VALUES (6,'Promethus','This is a very nice movie');
commit;

错误方法

ALTER TABLE TB_WITHOUT_DATA MODIFY description clob;
错误信息:

SQL Error: ORA-22858: invalid alteration of datatype
22858. 00000 - "invalid alteration of datatype"
*Cause: An attempt was made to modify the column type to object, REF,
nested table, VARRAY or LOB type.
*Action: Create a new column of the desired type and copy the current
column data to the new type using the appropriate type
constructor.

解决方法

方法一:对于此列没有数据的可通过以下方法修改-首先把该列改成Long类型,然后再改成clob类型

alter table TB_WITHOUT_DATA modify description long;--首先改成Long类型
alter table TB_WITHOUT_DATA modify description clob;--在Long类型的基础上改成clob类型

注:对于此列已经存在数据的,不能通过此方法,否则会报如下错误:

alter table TB_WITH_DATA modify description long;--更改包含数据的列
SQL Error: ORA-01439: column to be modified must be empty to change datatype
01439. 00000 -  "column to be modified must be empty to change datatype"

方法二:此方法适合此列包含数据和此列不包含数据两种情况

步骤一:把原来表中该列重命名

alter table TB_WITHOUT_DATA rename column description to description_bak;
alter table TB_WITH_DATA rename column description to description_bak;

步骤二:在表中增加该列,并指定改列类型为clob

alter table TB_WITHOUT_DATA add description clob;
alter table TB_WITH_DATA add description clob;
步骤三:对此列包含数据的需要包数据从步骤一重命名列中拷出(对于此列没有数据的此步骤省略)
update TB_WITH_DATA set description=description_bak;
commit;
步骤四:删除步骤一中的备份列
alter table TB_WITHOUT_DATA drop column description_bak;
alter table TB_WITH_DATA drop column description_bak;
步骤五:验证

1) 表结构验证

DESC TB_WITHOUT_DATA
Name        Null Type          
----------- ---- ------------- 
ID               NUMBER        
NAME             VARCHAR2(100) 
DESCRIPTION      CLOB 

DESC TB_WITH_DATA
Name        Null Type          
----------- ---- ------------- 
ID               NUMBER        
NAME             VARCHAR2(100) 
DESCRIPTION      CLOB  
2) 数据验证
select * from TB_WITH_DATA;

        ID NAME                       DESCRIPTION                                     
---------- -------------------------- ------------------------------------------------
         1 David Louis                He is capable of resolving such kind of issue   
         2 German Noemi               She is very beatiful and charming               
         3 Oliver Queen               He is main actor in the Green Arrow             
         4 Mark Williams              He plays snooker very well                      
         5 Sita Rama Raju Kata        I do not know this guy                          
         6 Promethus                  This is a very nice movie                       

 6 rows selected 

方法三:此方法适合此列包含数据和此列不包含数据两种情况

在讲解方法三之前,需要包表恢复到准备阶段,由于时间关系,直接通过drop然后re-create方法,脚本如下:

drop table TB_WITHOUT_DATA;
drop table TB_WITH_DATA;

create table TB_WITHOUT_DATA
(
  id NUMBER,
  name VARCHAR2(100),
  description VARCHAR2(2000)
);

create table TB_WITH_DATA
(
  id NUMBER,
  name VARCHAR2(100),
  description VARCHAR2(2000)
);

insert into TB_WITH_DATA VALUES (1,'David Louis','He is capable of resolving such kind of issue');
insert into TB_WITH_DATA VALUES (2,'German Noemi','She is very beatiful and charming');
insert into TB_WITH_DATA VALUES (3,'Oliver Queen','He is main actor in the Green Arrow');
insert into TB_WITH_DATA VALUES (4,'Mark Williams','He plays snooker very well');
insert into TB_WITH_DATA VALUES (5,'Sita Rama Raju Kata','I do not know this guy');
insert into TB_WITH_DATA VALUES (6,'Promethus','This is a very nice movie');
commit;
步骤一:重命名两张表
rename TB_WITHOUT_DATA to TB_WITHOUT_DATA_BAK;
rename TB_WITH_DATA to TB_WITH_DATA_BAK;
步骤二:创建两张新表(通过以下语句创建两张表)
create table TB_WITHOUT_DATA
as
select id, name, to_clob(description) description
from TB_WITHOUT_DATA_BAK;

create table TB_WITH_DATA
as
select id, name, to_clob(description) description
from TB_WITH_DATA_BAK;
表结构与数据验证:
desc TB_WITHOUT_DATA
Name        Null Type          
----------- ---- ------------- 
ID               NUMBER        
NAME             VARCHAR2(100) 
DESCRIPTION      CLOB

desc TB_WITH_DATA
Name        Null Type          
----------- ---- ------------- 
ID               NUMBER        
NAME             VARCHAR2(100) 
DESCRIPTION      CLOB 

select * from TB_WITH_DATA;

select * from TB_WITH_DATA;

        ID NAME                       DESCRIPTION                                     
---------- -------------------------- ------------------------------------------------
         1 David Louis                He is capable of resolving such kind of issue   
         2 German Noemi               She is very beatiful and charming               
         3 Oliver Queen               He is main actor in the Green Arrow             
         4 Mark Williams              He plays snooker very well                      
         5 Sita Rama Raju Kata        I do not know this guy                          
         6 Promethus                  This is a very nice movie                       

 6 rows selected 
步骤三:删除备份表:
DROP TABLE TB_WITHOUT_DATA_BAK;
DROP TABLE TB_WITH_DATA_BAK;

-----------------------------------------------------------------------------------------------------------------------------------------------------------

如果您们在尝试的过程中遇到什么问题或者我的代码有错误的地方,请给予指正,非常感谢!

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