1、删除列
03:44:40 SQL> create table test as select * from emp;
Table created.
03:45:06 SQL> desc test;
Name Null Type
---------------------------------------------------------------------- -------- -----------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)
03:45:10 SQL> alter table test drop column comm;
Table altered.
03:45:26 SQL> desc test;
Name Null Type
---------------------------------------------------------------------- -------- -----------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
DEPTNO NUMBER(2)
03:45:28 SQL> alter table test drop (sal,hiredate);
Table altered.
03:45:54 SQL> desc test;
Name Null Type
---------------------------------------------------------------------- -------- -----------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
DEPTNO NUMBER(2)
2、使用unused 删除列
将列标记为UNUSED，然后再数据库空闲时删除列
03:48:40 SQL> alter table test set unused column mgr;
Table altered.
03:49:03 SQL> desc test;
Name Null Type
---------------------------------------------------------------------- -------- -----------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
DEPTNO NUMBER(2)
03:49:04 SQL> alter table emp drop unused columns checkpoint 1000;
Table altered.
03:49:26 SQL>
Checkpoint 1000 用于指定每删除1000行发出一次检查点。
CUUG
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