ORACLE SQL 其它数据库对象
第十二章:其它数据库对象
序列:数据产生器
创建序列:
create sequence s1 start with 7936;
查看序列信息:
select * from user_sequences;
使用序列:
insert into emp (empno) values (s1.nextval);
修改序列:
注意：序列的start with 不能被修改!
alter sequence s1 increment by 10;
查看序列当前值:
注意：刚刚创建的序列在没有初始化的时候没有当前值！
select s1.currval from dual;
select s1.nextval from dual;
删除序列:
drop sequence s1;
索引:通过rowid实现的快速检索
对象号 文件号 块号 行号
AAAMfM AAE AAAAAg AAI
OOOOOO FFF BBBBBB RRR
A - Z a - z 0 - 9 + /
0 - 25 26 - 51 52 - 61 62 63
AAAM0a AAE AAAAAc AAA
M*64*64 + O*64 + 26 =
select
dbms_rowid.ROWID_OBJECT(rowid) oooooo,
dbms_rowid.ROWID_RELATIVE_FNO(rowid) fff,
dbms_rowid.ROWID_BLOCK_NUMBER(rowid) bbbbbb,
dbms_rowid.ROWID_ROW_NUMBER(rowid) rrr,
rowid,empno
from emp;
自动创建索引（由主键或唯一键约束创建）:
drop table e purge;
create table e as select * from emp;
select index_name from user_indexes where table_name='E';
alter table e add constraint pk_e_empno primary key (empno);
alter table e add constraint uk_e_ename unique(ename);
主键和唯一键有隐式的创建索引的动作！前提是启用约束时当前列没有索引！
手工创建索引：
create index i_e_job on e (job);
create index i_e_2 on e (empno,job,sal);
select index_name,table_name,column_name from user_ind_columns;
基于函数的索引:
create index scott.i_e_ename on e (lower(ename));
监控索引的使用:
alter index UK_E_ENAME monitoring usage;
select * from v$object_usage;
select * from e where lower(ename)='scott';
select * from v$object_usage;
select * from e where ename='SCOTT';
select * from v$object_usage;
create index i_e_ename on e (lower(ename));
alter index i_e_ename monitoring usage;
select * from e where lower(ename)='scott';
alter index UK_E_ENAME nomonitoring usage;
删除索引:
drop index i_e_ename;
分析索引结构有效性:
analyze index i_e_ename validate structure;
查看索引结构:
select NAME,HEIGHT,BLOCKS,BR_BLKS,BR_ROWS,LF_BLKS,LF_ROWS from index_stats;
合并索引叶级块碎片:
alter index i_e_ename coalesce;
重建索引:
alter index i_e_ename rebuild;
alter index i_e_ename rebuild online;
同义词:复杂对象名称的别名!
私有同义词:只有自己能用，不能和本方案下的表同名
创建私有同义词:
conn system/oracle
select * from scott.emp;
create synonym emp for scott.emp;
有了同义词就可以使用emp代替scott.emp
select * from emp;
show user
USER is "SYSTEM"
SQL> conn / as sysdba
Connected.
SQL> show user
USER is "SYS"
select * from emp;
删除私有同义词:
conn system/oracle
drop synonym emp;
create table emp (i int);
insert into emp values (1982);
commit;
create synonym emp for scott.emp;
ERROR at line 1:
ORA-00955: name is already used by an existing object
共有同义词:所有用户都能用，可以和本方案下的表同名，但表的优先级别高于同义词
创建公有同义词:
create public synonym emp for scott.emp;
select * from emp;
I
----------
1982
select * from scott.emp;
conn / as sysdba
select * from emp;
删除共有同义词:
conn system/oracle
drop public synonym emp;