Oracle高级 同义词 索引 序列

--同义词创建的语法
/*
CREATE [OR REPLACE] [PUBLIC] SYNONYM [schema .] synonym 
FOR [schema .] object [@ dblink];
*/

--同义词的优点
--1.安全，隐藏了数据库对象的名称和所有者
--2.提供了对象的公共访问
--3.简化了SQL语句

--查询emp表，但是不想让人知道查询的表的真实的名字  grant create synonym to scott ;      create synonym ep for emp;--数据字典查看同义词是否创建select * from user_synonyms;select * from ep;--创建一个dept表的同义词 dpcreate or replace synonym dp for dept;select * from user_synonyms;select * from dp;grant create public synonym to scott ;--为emp表创建一个公有的同义词 epcreate or replace public synonym ep for emp;--赋予权限创建同义词grant create [public] synonym to scott ;--同义词执行DMLinsert into dp values(58,'销售','衡阳');--删除同义词的权限grant drop public synonym to scott;--删除同义词drop public synonym ep;

--索引

create table student(       sid number,       sname varchar2(20))

create sequence seq_stu;

--批量插入insert into tableName 子查询;

--生成一条数据select seq_stu.nextval,dbms_random.string('1',10) from dual connect by level <=1;

--生成20条数据select seq_stu.nextval,dbms_random.string('1',10) from dual connect by level <=20;

--生成100W条数据insert into student select seq_stu.nextval,dbms_random.string('1',10) from dual connect by level <=1000000;

select count(1) from student;

--查询id为999999的数据select * from student s where s.sid=999999;--0.156s

--索引创建的语法

--创建索引create index ind_sid on student(sid);

select * from student s where s.sid=999999;--0.141s--数据字典查看索引

select * from user_indexes;

--查看DBA 用户下的索引

select * from dba_indexes where owner='SCOTT';

select * from dba_sequences;

--序列创建的语法

/*CREATE SEQUENCE [schema .] sequence[{ { INCREMENT BY | START WITH } 

integer | { MAXVALUE integer | NOMAXVALUE } | { MINVALUE integer | NOMINVALUE } | { CYCLE | NOCYCLE } | { CACHE integer | NOCACHE } | { ORDER | NOORDER } }  [ { INCREMENT BY | START WITH } integer | { MAXVALUE integer | NOMAXVALUE } | { MINVALUE integer | NOMINVALUE } | { CYCLE | NOCYCLE } | { CACHE integer | NOCACHE } | { ORDER | NOORDER }  ]...];*/

--创建一个序列  seq_test  起始值为1000   最大值为1004 步长为1的 不循环 缓存为20 的序列

create sequence seq_test start with 1000  maxvalue 1004 increment by 1 nocycle cache 20;

--怎么查看序列是否创建成功

--1.plsql左侧视图查看

--2.使用数据字典

select * from user_sequences;

--查看序列的值

select seq_test.nextval from dual;

--查看序列的下一个值

select seq_test.currval from dual;--序列当前值

create sequence seq_test1 start with 1000  maxvalue 1004 increment by 1 cycle cache 20;select seq_test1.nextval from dual;