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浅谈数据库联合查询

要理解join语句,首先得明白笛卡尔乘积(即集合的乘运算),其定义如下:
笛卡尔(Descartes)乘积又叫直积。假设集合A={a,b},集合B={1,2},则两个集合的笛卡尔积为{(a,1),(a,2),(b,1), (b,2)}。


 以下是Oracle自带的Scott用户下的Demo库的SQL

CREATE TABLE DEPT (    DEPTNO NUMBER(2) CONSTRAINT PK_DEPT PRIMARY KEY,    DNAME VARCHAR2(14),    LOC VARCHAR2(13)    );INSERT INTO DEPT VALUES (10,ACCOUNTING,NEW YORK);INSERT INTO DEPT VALUES (20,RESEARCH,DALLAS);INSERT INTO DEPT VALUES (30,SALES,CHICAGO);INSERT INTO DEPT VALUES (40,OPERATIONS,BOSTON);CREATE TABLE EMP (    EMPNO NUMBER(4) CONSTRAINT PK_EMP PRIMARY KEY,    ENAME VARCHAR2(10),    JOB VARCHAR2(9),    MGR NUMBER(4),    HIREDATE DATE,    SAL NUMBER(7,2),    COMM NUMBER(7,2),    DEPTNO NUMBER(2) CONSTRAINT FK_DEPTNO REFERENCES DEPT    );INSERT INTO EMP VALUES (7369,SMITH,CLERK,7902,to_date(17-12-1980,dd-mm-yyyy),800,NULL,20);INSERT INTO EMP VALUES (7499,ALLEN,SALESMAN,7698,to_date(20-2-1981,dd-mm-yyyy),1600,300,30);INSERT INTO EMP VALUES (7521,WARD,SALESMAN,7698,to_date(22-2-1981,dd-mm-yyyy),1250,500,30);INSERT INTO EMP VALUES (7566,JONES,MANAGER,7839,to_date(2-4-1981,dd-mm-yyyy),2975,NULL,20);INSERT INTO EMP VALUES (7654,MARTIN,SALESMAN,7698,to_date(28-9-1981,dd-mm-yyyy),1250,1400,30);INSERT INTO EMP VALUES (7698,BLAKE,MANAGER,7839,to_date(1-5-1981,dd-mm-yyyy),2850,NULL,30);INSERT INTO EMP VALUES (7782,CLARK,MANAGER,7839,to_date(9-6-1981,dd-mm-yyyy),2450,NULL,10);INSERT INTO EMP VALUES (7788,SCOTT,ANALYST,7566,to_date(13-JUL-87)-85,3000,NULL,20);INSERT INTO EMP VALUES (7839,KING,PRESIDENT,NULL,to_date(17-11-1981,dd-mm-yyyy),5000,NULL,10);INSERT INTO EMP VALUES (7844,TURNER,SALESMAN,7698,to_date(8-9-1981,dd-mm-yyyy),1500,0,30);INSERT INTO EMP VALUES (7876,ADAMS,CLERK,7788,to_date(13-JUL-87)-51,1100,NULL,20);INSERT INTO EMP VALUES (7900,JAMES,CLERK,7698,to_date(3-12-1981,dd-mm-yyyy),950,NULL,30);INSERT INTO EMP VALUES (7902,FORD,ANALYST,7566,to_date(3-12-1981,dd-mm-yyyy),3000,NULL,20);INSERT INTO EMP VALUES (7934,MILLER,CLERK,7782,to_date(23-1-1982,dd-mm-yyyy),1300,NULL,10);CREATE TABLE BONUS (    ENAME VARCHAR2(10),    JOB VARCHAR2(9),    SAL NUMBER,    COMM NUMBER    );CREATE TABLE SALGRADE (     GRADE NUMBER,    LOSAL NUMBER,    HISAL NUMBER    );INSERT INTO SALGRADE VALUES (1,700,1200);INSERT INTO SALGRADE VALUES (2,1201,1400);INSERT INTO SALGRADE VALUES (3,1401,2000);INSERT INTO SALGRADE VALUES (4,2001,3000);INSERT INTO SALGRADE VALUES (5,3001,9999);

 根据Oracle数据库scott模式下的emp表和dept表,完成下列题目。

1)    查询20号部门的所有员工信息。select * from emp where deptno = 20;(2)    查询所有工种为CLERK的员工的工号、员工名和部门名。select empno,ename,deptno from emp where job like CLERK;(3)    查询奖金(COMM)高于工资(SAL)的员工信息。select * from emp where comm > sal;(4)    查询奖金高于工资的20%的员工信息。select * from emp where comm > (sal*0.2);(5)    查询10号部门中工种为MANAGER和20号部门中工种为CLERK的员工的信息。select * from emp where (deptno = 10 and job like MANAGER) or (deptno = 20 and job like CLERK);(6)    查询所有工种不是MANAGER和CLERK,且工资大于或等于2000的员工的详细信息。select * from emp where job not in (MANAGER,CLERK) and sal >= 2000 ;(7)    查询有奖金的员工的不同工种。select distinct job from emp where comm is not null;(8)    查询所有员工工资和奖金的和。select ename,(sal+nvl(comm,0)) salcomm from emp;(9)    查询没有奖金或奖金低于100的员工信息。select * from emp where (comm is null or comm < 100) ;(10)    查询各月倒数第2天入职的员工信息。select * from emp where hiredate in (select (last_day(hiredate)-1) from emp);(11)    查询员工工龄大于或等于10年的员工信息。select * from emp where (sysdate - hiredate)/365 >= 10 ;(12)    查询员工信息,要求以首字母大写的方式显示所有员工的姓名。select upper(substr(ename,1,1)) || lower(substr(ename,2,length(ename)-1)) from emp;(13)    查询员工名正好为6个字符的员工的信息。select * from emp where length(ename)= 6 ;(14)    查询员工名字中不包含字母“S”员工。select * from emp where ename not in (select ename from emp where ename like %S%) ;select * from emp where ename not like%S%’;(15)    查询员工姓名的第2个字母为“M”的员工信息。select * from emp where ename like _M%;(16)    查询所有员工姓名的前3个字符。select substr(ename,1,3) from emp ;(17)    查询所有员工的姓名,如果包含字母“s”,则用“S”替换。select replace(ename,s,S) from emp ;(18)    查询员工的姓名和入职日期,并按入职日期从先到后进行排列。select ename,hiredate from emp order by hiredate asc ;(19)    显示所有的姓名、工种、工资和奖金,按工种降序排列,若工种相同则按工资升序排列。select ename,job,sal,comm from emp order by job desc,sal asc ;(20)    显示所有员工的姓名、入职的年份和月份,若入职日期所在的月份排序,若月份相同则按入职的年份排序。select ename,to_char(hiredate,yyyy)||-||to_char(hiredate,mm) from emp order by to_char(hiredate,mm),to_char(hiredate,yyyy);(21)    查询在2月份入职的所有员工信息。select * from emp where to_char(hiredate,mm) = 2 ;(22)    查询所有员工入职以来的工作期限,用“******日”的形式表示。select ename,floor((sysdate-hiredate)/365)||||floor(mod((sysdate-hiredate),365)/30)||||cell(mod(mod((sysdate-hiredate),365),30))|| from emp ;(23)    查询至少有一个员工的部门信息。select * from dept where deptno in (select distinct deptno from emp where mgr is not null) ;(24)    查询工资比SMITH员工工资高的所有员工信息。select * from emp where sal > (select sal from emp where ename like SMITH) ;(25)    查询所有员工的姓名及其直接上级的姓名。select staname,ename supname from (select ename staname,mgr from emp) t join emp on t.mgr=emp.empno ;(26)    查询入职日期早于其直接上级领导的所有员工信息。select * from emp where empno in (select staempno from (select empno staempno,hiredate stahiredate,mgr from emp) t join emp on t.mgr=emp.empno and stahiredate < hiredate) ;(27)    查询所有部门及其员工信息,包括那些没有员工的部门。select * from dept left join emp on emp.deptno=dept.deptno order by dept.deptno ;(28)    查询所有员工及其部门信息,包括那些还不属于任何部门的员工。(29)    查询所有工种为CLERK的员工的姓名及其部门名称。select ename,dname from emp join dept on job like CLERK and emp.deptno=dept.deptno ;(30)    查询最低工资大于2500的各种工作。select job from (select min(sal) min_sal,job from emp group by job) where min_sal > 2500 ;(31)    查询最低工资低于2000的部门及其员工信息。select * from emp where deptno in (select deptno from (select min(sal) min_sal,deptno from emp group by deptno) where min_sal < 2000) ;(32)    查询在SALES部门工作的员工的姓名信息。select ename from emp where deptno = (select deptno from dept where dname like SALES);(33)    查询工资高于公司平均工资的所有员工信息。select * from emp where sal > (select avg(sal) from emp) ;(34)    查询与SMITH员工从事相同工作的所有员工信息。select * from emp where job in (select job from emp where ename like SMITH) and ename not like SMITH ;(35)    列出工资等于30号部门中某个员工工资的所有员工的姓名和工资。select ename,sal from emp where sal =any (select sal from emp where deptno = 30) ;(36)    查询工资高于30号部门中工作的所有员工的工资的员工姓名和工资。select ename,sal from emp where sal >all (select sal from emp where deptno = 30) ;(37)    查询每个部门中的员工数量、平均工资和平均工作年限。select dname,count,avg_sal,avg_date from dept join (select count(*) count,avg(sal) avg_sal,avg((sysdate-hiredate)/365) avg_date,deptno from emp group by deptno) t on dept.deptno = t.deptno ;(38)    查询从事同一种工作但不属于同一部门的员工信息。select distinct t1.empno,t1.ename,t1.deptno from emp t1 join emp t2 on t1.job like t2.job and t1.deptno <> t2.deptno ;(39)    查询各个部门的详细信息以及部门人数、部门平均工资。Select dept.*,person_num,avg_sal from dept,(select count(*) person_num,avg(sal) avg_sal,deptno from emp group by deptno) t where dept.deptno = t.deptno ;(40)    查询各种工作的最低工资。select job,min(sal) from emp group by job ;(41)    查询各个部门中的不同工种的最高工资。select max(sal),job,deptno from emp group by deptno,job order by deptno,job ;(42)    查询10号部门员工以及领导的信息。select * from emp where empno in (select mgr from emp where deptno=10) or deptno = 10 ;(43)    查询各个部门的人数及平均工资。select deptno,count(*),avg(sal) from emp group by deptno ;(44)    查询工资为某个部门平均工资的员工信息。select * from emp where sal in (select avg(sal) avg_sal from emp group by deptno) ;(45)    查询工资高于本部门平均工资的员工的信息。select emp.* from emp join (select deptno,avg(sal) avg_sal from emp group by deptno) t on emp.deptno=t.deptno and sal>avg_sal ;(46)    查询工资高于本部门平均工资的员工的信息及其部门的平均工资。select emp.*,avg_sal from emp join (select deptno,avg(sal) avg_sal from emp group by deptno) t on emp.deptno=t.deptno and sal>avg_sal ;(47)    查询工资高于20号部门某个员工工资的员工的信息。select * from emp where sal >any(select sal from emp where deptno=20);(48)    统计各个工种的人数与平均工资。select job,count(*),avg(sal) from emp group by job ;(49)    统计每个部门中各个工种的人数与平均工资。select deptno,job,count(*),avg(sal) from emp group by deptno,job order by deptno,job;(50)    查询工资、奖金与10 号部门某个员工工资、奖金都相同的员工的信息。select emp.* from emp join (select sal,comm from emp where deptno = 10) t on emp.sal=t.sal and nvl(emp.comm,0)=nvl(t.comm,0) and emp.deptno != 10;(51)    查询部门人数大于5的部门的员工的信息。select * from emp where deptno in (select deptno from emp group by deptno having count(*)>5);(52)    查询所有员工工资都大于1000的部门的信息。select * from dept where deptno in (select distinct deptno from emp where deptno not in (select distinct deptno from emp where sal < 1000)) ;(53)    查询所有员工工资都大于1000的部门的信息及其员工信息。select * from emp join dept on dept.deptno in (select distinct deptno from emp where deptno not in (select distinct deptno from emp where sal < 1000)) and dept.deptno=emp.deptno;(54)    查询所有员工工资都在900~3000之间的部门的信息。select * from dept where deptno in (select distinct deptno from emp where deptno not in (select distinct deptno from emp where sal not between 900 and 3000)) ;(55)    查询所有工资都在900~3000之间的员工所在部门的员工信息。select * from emp where deptno in (select distinct deptno from emp where deptno not in (select distinct deptno from emp where sal not between 900 and 3000)) ;(56)    查询每个员工的领导所在部门的信息。select * from (select e1.empno,e1.ename,e1.mgr mno,e2.ename mname,e2.deptno from emp e1 join emp e2 on e1.mgr=e2.empno) t join dept on t.deptno=dept.deptno ;(57)    查询人数最多的部门信息。select * from dept where deptno in (select deptno from (select count(*) count,deptno from emp group by deptno) where count in (select max(count) from (select count(*) count,deptno from emp group by deptno)));(58)    查询30号部门中工资排序前3名的员工信息。select * from emp where empno in (select empno from (select empno,sal from emp where deptno=30 order by sal desc) where rownum < 4) ;(59)    查询所有员工中工资排在5~10名之间的员工信息。select * from emp where empno in (select empno from (select empno,rownum num from (select empno,sal from emp order by sal desc)) where num between 5 and 10 ) ;select empno from (select empno,sal from emp order by sal desc) where rownum <= 10 minus select empno from (select empno,sal from emp order by sal desc) where rownum < 5 ;(60)    查询SMITH员工及所有其直接、间接下属员工的信息。(61)    查询SOCTT员工及其直接、间接上级员工的信息。(62)    以树状结构查询所有员工与领导之间的层次关系。(63)    向emp表中插入一条记录,员工号为1357,员工名字为oracle,工资为2050元,部门号为20,入职日期为2002年5月10日。insertinto emp(empno,ename,sal,deptno,hiredate) values (1357,oracle,2050,20,to_date(2002年5月10日,yyyy"年"mm"月"dd"日")) ;(64)    向emp表中插入一条记录,员工名字为FAN,员工号为8000,其他信息与SMITH员工的信息相同。(65)    将各部门员工的工资修改为该员工所在部门平均工资加1000。update emp t1 set sal = (select new_sal from (select avg(sal)+1000 new_sal,deptno from emp group by deptno) t2 wher e t1.deptno = t2.deptno ) ;

浅谈数据库联合查询