Complex queries in sql
Download as DOCX, PDF3 likes1,680 views
This document provides SQL queries to solve common interview questions involving complex queries on tables. Some examples include queries to retrieve alternate records, find the nth highest or lowest salaries, select the first or last n records, find records that exist in one table but not another, and aggregate functions like counts and sums grouped by columns.
Complex queries in sql
- 1. Complex Queries in SQL ( Oracle ) 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?
- 2. 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 ‘S’ 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 ‘R’. 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)
- 3. 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