Difference between Abstract class and Interfaces.

Abstract class:

Abstract class comes under partial abstraction.
Abstract classes can maintain abstract methods and non abstract methods.
In abstract classes, we can create the variables.
In abstract classes, we can use any access specifier.
By using 'extends' keyword we can access the abstract class features from derived class.
Multiple inheritance is not possible.

Interface:

Interface comes under fully abstraction.
Interfaces can maintain only abstract methods.
In interfaces, we can't create the variables.
In interface, we can use only public access specifier.
By using 'implement' keyword we can get interface from derived class.
By using interfaces multiple inheritance is possible.

How to find out Max Salary from each department

You can find maximum salary for each department by grouping all records by DeptId and then using MAX() function to calculate maximum salary in each group or each department. SQL Query: SELECT DeptID, MAX(Salary) FROM Employee GROUP BY DeptID. This questions become more interesting if Interviewer will ask you to print department name instead of department id, in that case you need to join Employee table with Department using foreign key DeptID, make sure you do LEFT or RIGHT OUTER JOIN to include departments without any employee as well. Here is the query

List the emps who joined before 1981.

Answer: select * from emp where hiredate < (’01-jan-81’);

SQL Info

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