Oracle 列由VARCHAR2改为CLOB类型
最近突然遇到好多Oracle 列由VARCHAR2改为CLOB类型的需求，不知道大家是不是约好了。。。查了一些网上的文章，结合实际修改的情况记录一下各种场景及解决方法。
一、 示例准备
新建两张表TB_WITHOUT_DATA（VARCHAR2列不包含数据）和TB_WITH_DATA（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.
二、 解决方法
1. 待修改列无数据
- 列上无约束
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"- 列上有约束
如果列上有约束改为long类型也会报错
解决方法：
1）删除约束后再改，改完再建约束。
2）既然都是空的，drop掉这列直接加个clob类型列就好了，记得把约束建回去（建议先建测试表试下导入数据是否有问题）
2. 待修改列包含数据
注意此方法需要停业务，不然新数据会丢。当然不包含数据也可以用这种，但没必要。
1）重命名原列
alter table TB_WITHOUT_DATA rename column description to description_bak;
alter table TB_WITH_DATA rename column description to description_bak;2）新建clob列
alter table TB_WITHOUT_DATA add description clob;
alter table TB_WITH_DATA add description clob;3）将原列中数据更新到clob列
update TB_WITH_DATA set description=description_bak;
commit;4）删除原列
alter table TB_WITHOUT_DATA drop column description_bak;
alter table TB_WITH_DATA drop column description_bak;5）验证
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 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
3. 待修改列包含数据，另一种方法
注意此方法需要停业务，不然新数据会丢。当然不包含数据也可以用这种，但没必要。
1）重命名业务表
alter table TB_WITH_DATA rename to TB_WITH_DATA_BAK;2）通过以下语句创建新表
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_WITH_DATA
Name Null Type
----------- ---- -------------
ID NUMBER
NAME VARCHAR2(100)
DESCRIPTION CLOB
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 3）删除备份表
DROP TABLE TB_WITH_DATA_BAK;
参考
https://blog.csdn.net/jssg_tzw/article/details/40829867