- --1、非空约束遗失
- -->使用create table as 来创建对象
- scott@CNMMBO> create table tb_dept as select * from dept where 1=0;
- Table created.
- scott@CNMMBO> desc dept;
- Name Null? Type
- ----------------------------------------------------- -------- ------------------------------------
- DEPTNO NOT NULL NUMBER(2)
- DNAME VARCHAR2(14)
- LOC VARCHAR2(13)
- scott@CNMMBO> desc tb_dept;
- Name Null? Type
- ----------------------------------------------------- -------- ------------------------------------
- DEPTNO NUMBER(2)
- DNAME VARCHAR2(14)
- LOC VARCHAR2(13)
- -->从上面的desc可以看出新创建的表少了非空约束
- -->下面手动为其增加非空约束,增加后与原来的表是一致的。当然使用create table as时,索引是需要单独重建的。
- scott@CNMMBO> alter table tb_dept modify (deptno not null);
- Table altered.
- scott@CNMMBO> drop table tb_dept; -->删除刚刚穿件的表tb_dept
- Table dropped.
- --2、存在非空约束时default约束遗失
- -->下面为表dept的loc列添加非空约束,且赋予default值
- scott@CNMMBO> alter table dept modify (loc default 'BeiJing' not null);
- Table altered.
- -->为原始表新增一条记录
- scott@CNMMBO> insert into dept(deptno,dname) select 50,'DEV' from dual;
- 1 row created.
- scott@CNMMBO> commit;
- Commit complete.
- -->下面的查询可以看到新增记录50的loc为缺省值'BeiJing'
- scott@CNMMBO> select * from dept;
- DEPTNO DNAME LOC
- ---------- -------------- -------------
- 10 ACCOUNTING NEW YORK
- 20 RESEARCH DALLAS
- 30 SALES CHICAGO
- 40 OPERATIONS BOSTON
- 50 DEV BeiJing
- -->再次使用create table as来创建对象
- scott@CNMMBO> create table tb_dept as select * from dept;
- Table created.
- -->从下面可知,由于列loc存在default值,所以此时not null约束被同时赋予
- scott@CNMMBO> desc tb_dept
- Name Null? Type
- ----------------------------------------------------- -------- ------------------------------------
- DEPTNO NUMBER(2)
- DNAME VARCHAR2(14)
- LOC NOT NULL VARCHAR2(13)
- scott@CNMMBO> select * from tb_dept;
- DEPTNO DNAME LOC
- ---------- -------------- -------------
- 10 ACCOUNTING NEW YORK
- 20 RESEARCH DALLAS
- 30 SALES CHICAGO
- 40 OPERATIONS BOSTON
- 50 DEV BeiJing
- -->为新创建的表新增记录
- -->新增时发现尽管not null约束生效,但原表上设定的default值不存在了
- scott@CNMMBO> insert into tb_dept(deptno,dname) select 60,'HR' from dual;
- insert into tb_dept(deptno,dname) select 60,'HR' from dual
- *
- ERROR at line 1:
- ORA-01400: cannot insert NULL into ("SCOTT"."TB_DEPT"."LOC")
- scott@CNMMBO> drop table tb_dept;
- Table dropped.
- --4、最彻底的解决办法
- scott@CNMMBO> select dbms_metadata.get_ddl('TABLE','DEPT') from dual;
- DBMS_METADATA.GET_DDL('TABLE','DEPT')
- --------------------------------------------------------------------------------
- CREATE TABLE "SCOTT"."DEPT"
- ( "DEPTNO" NUMBER(2,0),
- "DNAME" VARCHAR2(14),
- "LOC" VARCHAR2(13) DEFAULT 'BeiJing' NOT NULL ENABLE,
- CONSTRAINT "PK_DEPT" PRIMARY KEY ("DEPTNO")
- USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255
- STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
- PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
- TABLESPACE "GOEX_USERS_TBL" ENABLE,
- UNIQUE ("DNAME")
- USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
- STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
- PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
- TABLESPACE "GOEX_USERS_TBL" ENABLE
- ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
- STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
- PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
- TABLESPACE "GOEX_USERS_TBL"
- --5、演示环境
- scott@CNMMBO> select * from v$version where rownum<2;
- BANNER
- ----------------------------------------------------------------
- Oracle Database 10g Release 10.2.0.3.0 - 64bit Production
--6、演示结论
-->create table as 尽管会克隆表及数据,数据是完整的,但是结构部分仅仅是部分克隆
-->create table as 会使用表上的约束被遗失或出于非正常状态
-->create table as 时,表上的索引、触发器等不会被同时克隆
-->create table as 仅作测试使用,要得到完整的结构语句,还是使用dbms_metadata.get_ddl包
-->Author: Robinson Cheng
-->Blog: http://blog.csdn.net/robinson_0612