Oracle知识梳理

create tablespace user1 datefile '' size 20M //创建一个名为User1的表空间

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autoextend on//数据文件的可扩展性

autoextend off//关闭

autoextend on next 5M//指定数据文件的增长幅度

autoextend on next 5m maxsize 500M

//查看表空间是否创建成功

select file_name,tablespace_name from dba_data_files order by file_name

//查看表空间

select tablespace_name,status,allocation_type from dba_tablespaces

select user_id,username,default_tablespace from dba_users//修改数据库默认表空间的的SQL语句

alter tablespace default tablespace user1

alter tablespace user2 rename to user20

dorp tablespace user20 including contents and datafiles

//创建主键约束

create table student (student_id number primary key,student_name vachar2(20),student_birthday date,student_address vachar2(50),student_phone vachar2(20))

//建立外键

create table customers(customer_id number primary key,customers_name vachar2(50),customers_address vachar2(50),customers_phone vachar2(20),email vachar2(20))

create table orders(orders_id number primary key,customers_id number,goods_name vachar2(20),quantity number,unit vachar2(10))

alter table orders add constraint fk_orders_customer foreign key (customer_id) referemces customers (customer_id)

//创建视图

create table employees1(employee_id number primary key,first_name vachar2(4),last_name vachar2(4),province vachar2(10),city vachar2(10),salary number)

select text from user_views where view_name='VW_EMPLOYEES'

select *from VW_EMPLOYEES

//修改视图

create or replace view VW_EMPLOYEES as 

select employee_id,last_name||first_name as employee_name,province||'-'||city as location,salary from employees1

//删除视图

drop view VW_EMPLOYEES

//创建索引

create index idx orders(orders_id,goods_name)

函数

//截取字符串

select substr('1234567890',5,4) from dual;//第五位开始的四个字符

//获得字符串出现的位置

select instr('big big tiger','big') from dual;

itrim()//删除字符串首部空格

rtrim()//删除字符串尾部空格

current_timestamp()//返回当前会话时区的当前时间戳

current_times()//返回当前会话时区的当前日期

//in判式用于判断表的列值是否存在于列表（集合）中。而exists判式则可用于判断查询结果集合是否为空

//排名

select student_name,rank() over(orders by student_age) position from student;

//if else

set serverout on;

delete employee_num number;

begin

select count(*) into employee_num from t_employees where status="ACT";

if employees_num>0 then

dbms_output.put_line('存在记录');

else

dbms_output.put_line('不存在记录');

end if;

end;

//case when

declare employee_num number;

begin

select count(*) into employee_num from t_employees where status="ACT";//将数目存储到变量employee_num中

case

when employee_num>1 then

dbms_output.put_line('存在多条有效记录');

when employee_num=1 then

dbms_output.put_line('仅存在一条有效记录');

else

dbms_output.put_line('不存在记录');

end case;

end;

创建储存过程

create or replace procedure update_students

begin

update student set student_age=10;

commit;

end update_students;

//执行储存过程

excute update_students;

IN OUT 参数

create or replace procedure swap(in_out_param1 in out number,in_out_param2 in out number) as

begin

declare param number;

begin

param:=in_out_param1;

in_out_param1:=in_out_param2;

in_out_param2:=param;

end;

end;

树形查询

查询 

查找重复数据

select distinct month from t_salary//获得唯一性记录

order by //升序(asc)和降序(desc)排列

group by //用于对记录集合进行分组

having //对数据源进行条件过滤