当心 CREATE TABLE AS

    对 DBA 而言,CREATE TABLE AS 可谓是家常便饭,顺手拈来。需不知该方式虽然简单,但疏忽也容易导致意想不到的问题。笔者前阵子就碰上
了这样的事情。由于是对原表进行克隆,且数据存储在不同的表空间,因此毫不犹豫地使用了CREATE TABLE AS,结果在运行package时,error...

--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. --3、唯一约束遗失 scott@CNMMBO> alter table dept modify (dname unique); Table altered. scott@CNMMBO> create table tb_dept as select * from dept; Table created. scott@CNMMBO> insert into tb_dept select 60,'DEV','ShangHai' from dual; 1 row created. scott@CNMMBO> commit; Commit complete. 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 60 DEV ShangHai -->有关check约束与外键约束不再演示 --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

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转载于:https://www.cnblogs.com/ajuanabc/archive/2012/03/16/2462733.html

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