Complex Queries in SQL ( Oracle ) ----------------------------------------- Hai All, These questions are the most frequently asked in interviews. 1) To fetch ALTERNATE records from a table. (EVEN NUMBERED) select * from emp where rowid in (select decode(mod(rownum,2),0,rowid, null) from emp); 2) To select ALTERNATE records from a table. (ODD NUMBERED) select * from emp where rowid in (select decode(mod(rownum,2),0,null ,rowid) from emp); 3) Find the 3rd MAX salary in the emp table. select distinct sal from emp e1 where 3 = (select count(distinct sal) from emp e2 where e1.sal <= e2.sal); 4) Find the 3rd MIN salary in the emp table. select distinct sal from emp e1 where 3 = (select count(distinct sal) from emp e2where e1.sal >= e2.sal); 5) Select FIRST n records from a table. select * from emp where rownum <= &n; 6) Select LAST n records from a table select * from emp minus select * from emp where rownum <= (select count(*) - &n from emp); 7) List dept no., Dept name for all the departments in which there are no employees in the department. select * from dept where deptno not in (select deptno from emp); alternate solution: select * from dept a where not exists (select * from emp b where a.deptno = b.deptno); altertnate solution: select empno,ename,b.deptno,dname from emp a, dept b where a.deptno(+) = b.deptno and empno is null; 8) How to get 3 Max salaries ? select distinct sal from emp a where 3 >= (select count(distinct sal) from emp b where a.sal <= b.sal) order by a.sal desc; 9) How to get 3 Min salaries ? select distinct sal from emp a where 3 >= (select count(distinct sal) from emp b where a.sal >= b.sal); 10) How to get nth max salaries ? select distinct hiredate from emp a where &n = (select count(distinct sal) from emp b where a.sal >= b.sal); 11) Select DISTINCT RECORDS from emp table. select * from emp a where rowid = (select max(rowid) from emp b where a.empno=b.empno); 12) How to delete duplicate rows in a table? delete from emp a where rowid != (select max(rowid) from emp b where a.empno=b.empno); 13) Count of number of employees in department wise. select count(EMPNO), b.deptno, dname from emp a, dept b where a.deptno(+)=b.deptno group by b.deptno,dname; 14) Suppose there is annual salary information provided by emp table. How to fetch monthly salary of each and every employee? select ename,sal/12 as monthlysal from emp; 15) Select all record from emp table where deptno =10 or 40. select * from emp where deptno=30 or deptno=10; 16) Select all record from emp table where deptno=30 and sal>1500. select * from emp where deptno=30 and sal>1500; 17) Select all record from emp where job not in SALESMAN or CLERK. select * from emp where job not in ('SALESMAN','CLERK'); 18) Select all record from emp where ename in 'BLAKE','SCOTT','KING'and'FORD'. select * from emp where ename in('JONES','BLAKE','SCOTT','KING','FORD'); 19) Select all records where ename starts with â€˜Sâ€™ and its lenth is 6 char. select * from emp where ename like'S____'; 20) Select all records where ename may be any no of character but it should end with â€˜Râ€™. select * from emp where ename like'%R'; 21) Count MGR and their salary in emp table. select count(MGR),count(sal) from emp; 22) In emp table add comm+sal as total sal . select ename,(sal+nvl(comm,0)) as totalsal from emp; 23) Select any salary <3000 from emp table. select * from emp where sal> any(select sal from emp where sal<3000); 24) Select all salary <3000 from emp table. select * from emp where sal> all(select sal from emp where sal<3000); 25) Select all the employee group by deptno and sal in descending order. select ename,deptno,sal from emp order by deptno,sal desc; 26) How can I create an empty table emp1 with same structure as emp? Create table emp1 as select * from emp where 1=2; 27) How to retrive record where sal between 1000 to 2000? Select * from emp where sal>=1000 And sal<2000 28) Select all records where dept no of both emp and dept table matches. select * from emp where exists(select * from dept where emp.deptno=dept.deptno) 29) If there are two tables emp1 and emp2, and both have common record. How can I fetch all the recods but common records only once? (Select * from emp) Union (Select * from emp1) 30) How to fetch only common records from two tables emp and emp1? (Select * from emp) Intersect (Select * from emp1) 31) How can I retrive all records of emp1 those should not present in emp2? (Select * from emp) Minus (Select * from emp1) 32) Count the totalsa deptno wise where more than 2 employees exist. SELECT deptno, sum(sal) As totalsal FROM emp GROUP BY deptno HAVING COUNT(empno) > 2