Complex Queries in SQL ( Oracle )

Complex Queries in SQL ( Oracle )


These questions are the most frequently asked in interviews.

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);

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);

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);

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);

Select FIRST n records from a table.
select * from emp where rownum <= &n;

Select LAST n records from a table
select * from emp minus select * from emp where rownum <= (select count(*) - &n from emp);

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;

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;

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);

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);
Select DISTINCT RECORDS from emp table.
select * from emp a where  rowid = (select max(rowid) from emp b where  a.empno=b.empno);

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);

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;
 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;

Select all record from emp table where deptno =10 or 40.

select * from emp where deptno=30 or deptno=10;

Select all record from emp table where deptno=30 and sal>1500.

select * from emp where deptno=30 and sal>1500;

Select  all record  from emp where job not in SALESMAN  or CLERK.

select * from emp where job not in ('SALESMAN','CLERK');

Select all record from emp where ename in 'BLAKE','SCOTT','KING'and'FORD'.

select * from emp where ename in('JONES','BLAKE','SCOTT','KING','FORD');

Select all records where ename starts with ‘S’ and its lenth is 6 char.

select * from emp where ename like'S____';

Select all records where ename may be any no of  character but it should end with ‘R’.

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

Count  MGR and their salary in emp table.

select count(MGR),count(sal) from emp;

In emp table add comm+sal as total sal  .

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

Select  any salary <3000 from emp table.

select * from emp  where sal> any(select sal from emp where sal<3000);

Select  all salary <3000 from emp table.

select * from emp  where sal> all(select sal from emp where sal<3000);

Select all the employee  group by deptno and sal in descending order.

select ename,deptno,sal from emp order by deptno,sal desc;

How can I create an empty table emp1 with same structure as emp?

Create table emp1 as select * from emp where 1=2;

How to retrive record where sal between 1000 to 2000?
Select * from emp where sal>=1000 And  sal<2000

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)

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)

How to fetch only common records from two tables emp and emp1?
(Select * from emp) Intersect (Select * from emp1)

 How can I retrive all records of emp1 those should not present in emp2?
(Select * from emp) Minus (Select * from emp1)

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

SQL Tutorial

SQL (Structured Query Language) is used to modify and access data or information from a storage area called database. This beginner online training sql tutorial website teaches you the basics of SQL code and train you how to write & program SQL queries. I will be sharing my database knowledge on SQL and help you learn programming SQL better. The concepts discussed in this SQL tutorial can be applied to most of database systems. The SQL syntax used to explain the tutorial concepts is similar to the one used in Oracle database.

What is SQL?

• SQL stands for Structured Query Language
• SQL lets you access and manipulate databases
• SQL is an ANSI (American National Standards Institute) standard

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What Can SQL do?

• SQL can execute queries against a database
• SQL can retrieve data from a database
• SQL can insert records in a database
• SQL can update records in a database
• SQL can delete records from a database
• SQL can create new databases
• SQL can create new tables in a database
• SQL can create stored procedures in a database
• SQL can create views in a database
• SQL can set permissions on tables, procedures, and views

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SQL is a Standard - BUT....

Although SQL is an ANSI (American National Standards Institute) standard, there are different versions of the SQL language.

However, to be compliant with the ANSI standard, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

SQL Database Design

IBM first developed SQL in 1970s. Also it is an ANSI/ISO standard. It has become a Standard Universal Language used by most of the relational database management systems (RDBMS). Some of the RDBMS systems are: Oracle, Microsoft SQL server, Sybase etc. Most of these have provided their own implementation thus enhancing it's feature and making it a powerful tool.

SQL Commands: Few SQL Coding Statements?

Few of the sql commands used in sql code programming are:SELECT Statement, UPDATE Statement, INSERT INTO Statement,DELETE Statement, WHERE Clause, ORDER BY Clause, GROUP BY Clause, Subquery Clauses, Joins, Views, GROUP Functions,Indexes etc.