oracle----sql----查询---为例---计算

--ddl dml dcl dql

select *from emp e;--*代表所有列

select empno,ename from emp;--,分格例

select empno as id,ename as name from emp;

select empno "编号",ename"姓名"from emp;--特殊字符

select distinct deptno from emp;--去重复

---------* , as distinct

--固定值

select empno,sal,comm,8888888"红包"from emp;

--计算列

select empno,enma,sal||'美元'as money from emp;

--null运算(遇空为空)

select empno,ename,sal,comm,sal+comm+1 as money from emp;

--null运算(遇空为值)

select empno,ename,sal,comm,sal+nvl(comm,0) as money from emp;

--加减乘除运算

select ename,sal,(mod(sal+2-2)*2/2 ,100) as money from emp;

--升序

select empno,ename,sal,com from emp order by sal asc;

--降序

select empno,ename,sal,com from emp order by sal desc;

--根据放在desc前的列降序

select empno,ename,sal,com from emp order by sal,comm desc;

--根据运算结果降序

select empno,ename,sal,comm from emp order by sal+nvl(comm,0) desc;

---------------------------------------------------

--where 查询

--where快速寻找= > < >= <= <>不等

select*from emp where empno=7900;

--两者之间

select*from emp where sal>=1600 and sal<=3000;

select*from emp where sal between 1600 and 3000;

--或者

select*from emp where ename='JAMES' or ename='ADAMS' or ename='SMITH';

select*from emp where ename in('JAMES','ADAMS','SMITH');

select*from emp where substr(ename,1,1)='S';

--%任意一个(第一个S)

select*from emp where ename like 'S%'

--取不到它第一个s(少用)

select*from emp where ename not like 'S%'

select*from emp where not(ename like 'S%');

--第二个是s;

select*from emp where ename like '_S%';

--有个s就行

select*from emp where ename like '%S%';

update emp set ename='sm%mm_tom' where empno=7369;

--escape转移符号,找有%的

select*from emp where ename like '%\%%'escape'\';

--找有_的

select*from emp where ename like '%\_%' escape'\';

--寻找为空的

select*from emp where nvl(comm,0)=0;

select*from emp where comm is null;

-------------------------------------------------

--伪列(rowid)

select rowid,e.*from emp e;

select rownum,e.*from emp e;

select rownum,e.*from emp e where rownum<=10;

--不能直接用between.

select*from(select rownum num,e.*from emp e where rownum<=10) a where a.num>5;

--分组

select*from emp;

select distinct job from emp;

select job from emp group by job;

--统计函数

select

job,

count (empno) 人数 ,

sum(sal)工资,

avg(sal)平均,

max(sal)最大,

min(sal)最小

from emp

group by job;

--统计函数不统计null值

select

job,

count (empno) 人数 ,

sum(nvl(comm,0))工资,

avg(nvl(comm,0))平均,

max(nvl(comm,0))最大,

min(nvl(comm,0))最小

from emp

group by job;

--部门

select

deptno,

job,

count (empno) 人数 ,

sum(sal)工资,

avg(sal)平均,

max(sal)最大,

min(sal)最小

from emp

group by deptno,job,

--格式

order by deptno,job;

select

deptno,

count (empno) 人数 ,

sum(sal)工资,

avg(sal)平均,

max(sal)最大,

min(sal)最小

from emp

group by deptno

having sum(sal)>9000;

select

count (empno) 人数 ,

sum(sal)工资,

avg(sal)平均,

max(sal)最大,

min(sal)最小

from emp

-----------------------------------------

create or view v$student1(id,name,age)

--union all把表加起来

select 1,'tom01',19 from dual

union all

select 2,'tom02',20 from dual

union all

select 3,'tom03',30 from dual

select*from v$student1;

----------------------------------------

create or view v$student2(id,name,age)

--union all把表加起来(所有数据库通用)

--union删掉重复记录(顺序,遇到它以前重复都去重复)

select 1,'tom01',19 from dual

union all

select 2,'tom02',20 from dual

union

select 2,'tom02',20 from dual

union all

select 3,'tom03',30 from dual

select*from v$student2;

----------------------------------------

--交集--oracle sql专用

select*from v$student1

intersect

select*from v$student2;

------------------------------

--差集--oracle sql专用

select*from v$student1

minus

select*from v$student2;