[每日一题] OCP1z0-047 :2013-07-16 主键与唯一索引
2013-07-16 19:41
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主键包括非空和唯一约束,它会自动创建唯一索引(注:唯一约束也会自动创建唯一索引),测试如下:
1、 创建一个表products
gyj@OCM> Create table products(
2 product_id number(6) constraintprod_id_pk PRIMARY KEY,
3 product_name varchar2(15)
4 );
Table created.
2、 查表products的索引
gyj@OCM> select INDEX_NAME,INDEX_TYPE,UNIQUENESS fromuser_indexes where TABLE_NAME='PRODUCTS';
INDEX_NAME INDEX_TYPE UNIQUENES
------------------------------ --------------------------- ---------
PROD_ID_PK NORMAL UNIQUE
答案:B
补充:唯一约束也会自动创建唯一索引
gyj@OCM> create table t10 (id int unique,name varchar2(10));
Table created.
gyj@OCM> select INDEX_NAME,INDEX_TYPE,UNIQUENESS from user_indexes where TABLE_NAME='T10';
INDEX_NAME INDEX_TYPE UNIQUENES
------------------------------ --------------------------- ---------
SYS_C0011336 NORMAL UNIQUE
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