select sal from emp where empno=7839;
字符函數
select length(sal) from emp;
select lower(ename) from emp;
select upper(ename) from emp;
select substr(sal,1,3) from emp;
select replace(sal,'a','dddddddddddd') from emp;
select round(sal,1) from emp where empno=7839;
select comm from emp where empno=7839;
select trunc(comm) from emp where empno=7839;
select trunc(comm,1) from emp where empno=7839;
select ceil(comm) from emp wher+e empno=7839; ---向上取整
select floor(comm) from emp where empno=7839; --向下取整
select mod(10,3) from dual;
select floor(sal) from emp;
select sysdate from dual;
select * from emp where sysdate> add_months(hiredate,8*12); --- 工齡超過8年的
select trunc(sysdate-hiredate),ename from emp;
select hiredate,last_day(hiredate) from emp;
select hiredate ,ename from emp where last_day(hiredate)-2=hiredate; ---某個月的倒數第三天
select to_char(hiredate,'yyyy-MM-dd hh:mi:ss') from emp;
select to_char(hiredate,'yyyy-MM-dd hh24:mi:ss') from emp;
insert into emp values(8881,'testUser','manager',7782,sysdate,100,1000,10);
insert into emp values(8882,'testUser','manager',7782,to_date('2012-12-20 23:12:12','yyyy-MM-dd hh24:mi:ss'),100,1000,10);
commit;
select * from emp where empno=8882;
select to_char(sal,'L9,999.99') from emp;
select to_char(sal,'$9,999.99') from emp;
select ename,hiredate from emp where to_char(hiredate,'MM')=12; --查詢12月入職的員工
select ename,hiredate from emp where to_char(hiredate,'yyyy')=1980; --查詢1980 入職的員工
系統函數
select sys_context('USERENV','db_name') from dual;
select sys_context('USERENV','current_schema') from dual;
select sys_context('USERENV','language') from dual;
select sys_context('USERENV','session_user') from dual;
--只讀存儲過程是用來獲得，某個時間的數據
set transaction read only;
用戶和方案的關係
一個用戶對應一個方案，用戶以方案的方式管理 數據庫對象
一個方案包括 表 視圖 觸發器 存儲過程