oracle查询操作

##oracle查询操作

emp 员工表（empno 员工号/ename 员工姓名/job 工作/mgr 上级编号/hiredate 受雇日期/sal 薪金/comm 佣金/deptno 部门编号）
dept 部门表（deptno 部门编号/dname 部门名称/loc 地点）
 
---------------SELECT语句的完整查询 ---------------
--1.列描述
DESC EMP;
--2.检索所有列
Select * from EMP;
--3.检索特定列:员工号, 员工姓名
SELECT EMPNO, ENAME, JOB
  FROM EMP T;
--5.distinct 取消重复的行 ,显示不重复的工作
Select distinct job from emp;
--6.计算列,显示员工姓名，12月薪金
select ename,sal*12 from emp;
--7.列别名 员工姓名 别名“员工”
select ename "员工" from emp
--8.使用空值 
a.使用nvl和nvl2处理空值 
select ename,sal+NVL(comm,0) from emp;
select ename,comm,sal,NVL2(comm,sal+comm,sal) from emp;
--NVL2(E1, E2, E3)的功能为：如果E1为NULL，则函数返回E3，若E1不为null，则返回E2。
--9.使用连接字符串
select ename ||'工作是'||job from emp;
select concat(concat(ename, '工作是'),job) from emp


--注意结果为甚么和实际不同
SELECT JOB, SUM(T.SAL + T.COMM) INCOME
  FROM EMP T
 WHERE T.DEPTNO IN (2, 3)
 GROUP BY JOB;


SELECT JOB, SUM(T.SAL + T.COMM) INCOME
  FROM EMP T
 WHERE T.DEPTNO IN (2, 3)
 GROUP BY JOB HAVING SUM(T.SAL+T.COMM)>1000;

 
---------------关于WHERE查询条件使用 ---------------
--1.子句查询为数值 
select ename,sal from emp where sal > 2000
--2.子句查询为字符 
select ename,sal from emp where ename = 'SCOTT';
--3.子句查询为日期: 
select ename,sal from emp where hiredate= to_date(19801217,'yyyymmdd');
select ename,sal from emp where hiredate > to_date(19801217,'yyyymmdd');
--4.Between and 查询  
Select ename,sal,hiredate from emp where sal between 2000 and 3000
--5.LIKE 查询(通配符 %,_)
select ename,sal,hiredate from emp where ename like 'S%'
 select ename,sal,hiredate from emp where ename like '___T%'
--6.IN的使用
select ename,sal,hiredate from emp where sal in (800,3000);
--7.NULL值的判断
select ename,sal,hiredate,mgr from emp where mgr is null;(注意这里不能使用=null)
--8.AND OR NOT 使用(顺序 NOT > OR > AND)
select ename,sal,deptno,job from emp where deptno = 20 and job = 'CLERK';
select ename,sal,deptno,job from emp where deptno = 20 or job = 'CLERK';
---------------统计分析 ---------------
--ORDER BY 排序:
1.默认按升序排序(ASC)，这里NULL放最后
Select ename,sal,COMM from emp order by COMM;
Select ename,sal,COMM from emp order by COMM ASC;
2.降序排序 ，按佣金降序
Select ename,sal,COMM from emp order by COMM DESC;
3.多列排序， 
Select ename,sal,COMM from emp order by COMM DESC,SAL;
4.非选择列排序
Select ename,sal  from emp order by COMM DESC ;
5.使用别名排序  
Select ename,sal,COMM "奖金"  from emp order by "奖金" DESC ;
6.使用位置编号排序， 
Select ename,sal,COMM "奖金"  from emp order by  2 DESC ;
--group by 数据分组 
分组求最大，最小值
select max(sal),min(sal) from emp;
2.平均值，求和，数量
select max(sal),min(sal),sum(sal),avg(sal),count(sal) from emp
3.求总数
select count(comm) from emp;
Select count(distinct comm) from emp;
Select count(*) from emp;
--SELECT * FROM EMP FOR UPDATE
--having子句的使用
1.Group by 单列
select deptno,max(sal),avg(sal) from emp group by deptno;
2.Group by 多列
select deptno,job,max(sal),avg(sal) from emp group by deptno,job order by deptno,job;
3.Having 限制显示
select deptno,job,max(sal),avg(sal) from emp group by deptno,job having avg(sal) > 1000 order by deptno,job;
4.Order by 排序
select deptno,job,max(sal),avg(sal) from emp group by deptno,job having avg(sal) > 1000 order by avg(sal);
--报表排序
如果是ROLLUP(A, B, C)的话，首先会对(A、B、C)进行GROUP BY，然后对(A、B)进行GROUP BY，然后是(A)进行GROUP BY，最后对全表进行GROUP BY操作。
如果是GROUP BY CUBE(A, B, C)，则首先会对(A、B、C)进行GROUP BY，然后依次是(A、B)，(A、C)，(A)，(B、C)，(B)，(C)，最后对全表进行GROUP BY操作。 

1.Rollup 与 Cube 生成小计与总计：
SELECT DEPTNO, JOB, AVG(SAL) FROM EMP GROUP BY ROLLUP(DEPTNO, JOB);
SELECT DEPTNO, JOB, AVG(SAL)
	FROM EMP
 GROUP BY CUBE(DEPTNO, JOB)
 ORDER BY DEPTNO
---------------多表连接---------------
1.等值连接
--员工姓名，部门
SELECT ENAME, SAL, DNAME
    FROM EMP E, DEPT D
 WHERE E.DEPTNO = D.DEPTNO
 ORDER BY D.DEPTNO;
--1部门
SELECT ENAME, SAL, DNAME
    FROM EMP E, DEPT D
 WHERE E.DEPTNO = D.DEPTNO
     AND D.DEPTNO = 10

3.自连接
SELECT A.*, B.ENAME MNAME FROM EMP A, EMP B WHERE A.MGR = B.EMPNO ORDER BY  A.EMPNO
--某员工，层级关系
SELECT a.*, LEVEL
  FROM EMP A
CONNECT BY A.EMPNO = PRIOR MGR
 START WITH A.EMPNO = 7934

4.外连接
--公司员工信息 (左连接)
SELECT A.DNAME, B.ENAME, B.SAL FROM DEPT A LEFT JOIN EMP B ON A.Deptno = B.Deptno;
 --公司员工信息(右连接)
SELECT A.DNAME, B.ENAME, B.SAL FROM DEPT A RIGHT JOIN EMP B ON A.DEPTNO = B.DEPTNO  AND B.DEPTNO = 1;
 --公司员工信息(完全连接)
SELECT A.DNAME, B.ENAME, B.SAL FROM DEPT A
 FULL JOIN EMP B ON A.DEPTNO = B.DEPTNO AND A.DEPTNO = 1
5.子查询
--单行子查询
SELECT *
    FROM EMP
 WHERE DEPTNO = (SELECT DEPTNO FROM EMP WHERE ENAME = 'SCOTT')
     AND ENAME != 'SCOTT'
--多行子查询
SELECT * FROM EMP WHERE JOB IN (SELECT JOB FROM EMP WHERE DEPTNO = 10);
SELECT * FROM EMP WHERE sal >= ALL(SELECT sal FROM EMP WHERE DEPTNO = 30);
SELECT * FROM EMP WHERE sal >= ANY(SELECT sal FROM EMP WHERE DEPTNO = 30);
--相关子查询
EXISTS与IN的效率对比 
SELECT *
    FROM EMP A
 WHERE EXISTS (SELECT 1
                    FROM DEPT B
                 WHERE A.DEPTNO = B.DEPTNO
                     AND B.DNAME =  'ACCOUNTING')

SELECT *
  FROM EMP A
 WHERE a.DEPTNO in (SELECT B.DEPTNO FROM DEPT B WHERE B.DNAME = '技术部')
                     
--FROM子查询
SELECT ENAME, JOB, SAL
    FROM EMP, (SELECT DEPTNO, AVG(SAL) AVGSAL FROM EMP GROUP BY DEPTNO) DEPTSTD
 WHERE DEPTSTD.DEPTNO = EMP.DEPTNO
     AND EMP.SAL > DEPTSTD.AVGSAL
--DML子查询
--insert中使用子查询
INSERT INTO employee 
SELECT * FROM emp
--update中使用子查询
UPDATE emp SET (sal,comm) = (SELECT sal,comm FROM emp WHERE ename = 'SMITH')
WHERE job = (SELECT job  FROM emp WHERE ename = 'SMITH')
--delete 中使用子查询
DELETE FROM emp WHERE job = (SELECT job FROM emp WHERE ename='SMITH')
--DDL中使用子查询

--其它查询
-- Case when
SELECT ENAME,
       SAL,
       CASE
         WHEN SAL > 1500 THEN
          1
         WHEN SAL = 1500 THEN
          2
         ELSE
          2
       END GRADE
  FROM EMP
--With 子句
WITH EMPL AS (
  SELECT DEPTNO,AVG(SAL) AVG_SAL  FROM EMP GROUP BY DEPTNO
)
SELECT * FROM EMPL A WHERE AVG_SAL
 > (SELECT SUM(AVG_SAL)/3 FROM EMPL B )