oracle主键和索引

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  Case 1：先创建主键，再级联删除key，索引级联删除；

STEP 1. SQL >create table t1(x int, y int);

STEP 2. SQL >alter table t1 add (constraint pk_t1 primary key(x));

STEP 3. SQL >select INDEX_NAME,INDEX_TYPE,GENERATED,table_name from user_indexes where table_name='T1' ;

STEP   4. SQL> alter table t1 drop constraint pk_t1 cascade;     

STEP 5. SQL> select INDEX_NAME,INDEX_TYPE,GENERATED,table_name from user_indexes where table_name='T1' ;

      Case 2：  先创建索引 ，再创建key，查询后级联删除key，索引未删除；

STEP 1. SQL> create table t1(x int, y int);

STEP 2. SQL> create unique index pk_t1 on t1 (x);

STEP 3. SQL> alter table t1 add (constraint pk_t2 primary key(x));

STEP 4. SQL>  select OWNER,CONSTRAINT_NAME,CONSTRAINT_TYPE,TABLE_NAME,INDEX_OWNER,INDEX_NAME from  user_constraints where table_name = 'T1';

STEP 5. SQL> select INDEX_NAME,INDEX_TYPE,GENERATED,table_name from user_indexes where table_name='T1' ;

STEP 6. SQL> alter table t1 drop constraint pk_t2 cascade;

STEP 7. SQL> select INDEX_NAME,INDEX_TYPE,GENERATED,table_name from user_indexes where table_name='T1' ;  

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