oracle10g- oracle数据语言 常用函数 日期格式

数据语言 ddl create alter drop定义dcl grant revoke控制dml select delete update insert操作
create table tt(c1 varchar2(10),c2 varchar(6));
alter table tt add cc number;alter table tt drop column c2;
grant select on tt to scott;revoke select on tt from scott;
insert into tt values('dfs','ss');update tt set c2='dd' where c1='dfs';
select substr('01234567',1,4) from dual;//0123不支持left right函数 select substr('01234567',1,4) from dual //相当于leftselect substr ('01234567',length('01234567')-4+1,4) from dual; --相当于right

**************select sysdate from dual;设置时间 格式alter session set nls_date_fromat='dd-mon-yyyy hh:mi:ss';select next_day(sysdate,'星期三') from dual;//星期几不能是数字 像3 或星期3 表示从今天开始下一个星期三是哪一天
select to_char(sysdate,'yyyy-mm-dd') from dual;select to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual;select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;
select to_date('2010-3-2') from dual;select to_number('343') from dual;
select sum(decode(sex,'男',1,0)) 男生数,sum(decode(sex,'女',1,0)) 女生数 from tablename;

如果有的列有空值可以用其他数据来代替select id,nvl(name,'待输入') from t1;select id from t1 where name is null;//这里不能用=号select id from t1 where name is not null;
select * from t1 order by id asc;select * from t1 order by id desc;
select * from t1 exists (select * from t1);
select distinct name from t1;

select * from t1 exists (select * from t1 where t1.name is not null);oracle 中常用的系统函数1.字符 length,lengthb, ltrim. replace, rtrim, substr, trim.2.日期 sysdate current_date,next_day.3.转换 to_char ,to_date,to_number4.聚焦 sum,avg,max,min,count5.其他 user,decode,nvl
select lenght('司要民a') from dual;select ltrime(' ddd') from dual;select rtrime('ddd ') from dual;select trime(' ddd ') from dual; 常与varchar char 一块用
聚焦函数不能做为条件 写在where子句的后面
如 select pub from books where sum(price)>90 会报错应该这样写select pub from books group by pub heaving sum(price)>90;
select id ,name from t1 union 取并集select id,name from t2
select id ,name from t1interectselect id,name from t2//取交集
insert into t1(name) select name from t2;create tablet3 as (select id ,name from t3)