Hi Friend,

Consider the following table 'employee':

-------+----------+---------
| emp_id| emp_name| salary |
+-------+---------+---------
| 1 | AAAAAAAA| 2014 |
| 2 | BBBBBBBB| 4021 |
| 2 | CCCCCCCC| 22 |
| 4 | DDDDDDDD| 25 |
|
+-------+---------+--------+

1) The following query finds the second highest salary from the table employee:
SELECT MAX(salary) FROM employee WHERE salary NOT IN (SELECT MAX(salary) FROM employee);

2) The following query finds the second least salary from the table
employee:
SELECT MIN(salary) FROM employee WHERE salary NOT IN (SELECT MIN(salary) FROM employee);

3) The following query finds the duplicate rows from the table
employee according to emp_id:
SELECT *, count(*) as n FROM employee group by emp_id HAVING n>1;

Difference between SQL and PL/SQL:

SQL is a structured query language that allows direct interaction with the database.Sql provide queries(select,insert,update etc.), manipulate objects(DDL) and data(DML).

PL/SQL is a procedural language that includes all the features of other programming languages except the ability to easily integrate with SQL.

Differences:

1 SQL is executed one statement at a time. PL/SQL is executed as a block of code.
2 SQL tells the database what to do (declarative) while PL/SQL tell the database how to do things (procedural).
3 SQL is used to code queries, DML and DDL statements. PL/SQL is used to code program blocks, triggers, functions, procedures and packages.
4 You can embed SQL in a PL/SQL program, but you cannot embed PL/SQL within a SQL statement.

Thanks