SQL>create table test(id int,name varchar2(10));
Tablecreated
SQL>insert into test values(1,'a');
1row inserted
SQL>insert into test values(2,'b');
1row inserted
SQL>commit;
Commitcomplete
SQL>select * from test;
ID NAME
---------------------------------------
1 a
2 b
SQL> desc test
NameType Nullable Default Comments
---------------- -------- ------- --------
ID INTEGER Y
NAMEVARCHAR2(10) Y
SQL> alter table test modify(name clob);
altertable test modify (name clob)
ORA-22858: 数据类型的变更无效
如果直接转换，报错！
我们可以通过间接的方式来操作：
新建一个clob类型的列，将原列的值插入新建的列，然后删除原列，重命名新列。
SQL> alter table test add name1clob;
Table altered
SQL> update test setname1=name;
2rows updated
SQL> select * from test;
IDNAME NAME1
----------------------------------------------------------------------------------
1 a a
2 b b
SQL> desc test
Name Type Nullable Default Comments
----------------- -------- ------- --------
ID INTEGER Y
NAME VARCHAR2(10) Y
NAME1CLOB Y
SQL> commit;
Commit complete
SQL> alter table test dropcolumn name;
Table altered
SQL> alter table test renamecolumn name1 to name;
Table altered
SQL> select * from test;
ID NAME
---------------------------------------------------------------------
1 a
2 b
SQL> desc test
NameType Nullable Default Comments
----------- -------- ------- --------
ID INTEGER Y
NAMECLOB Y
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