My Thoughts & Views

Interfaces
–contain only abstract methods
–interface can’t be inherited from a class
–using interfaces we can achieve multiple inheritance
–doesn’t allow accessibility modifiers (Public/Private/Internal)
–can’t contain fields, constructors
–is must implementable & its scope is upto any level of its inheritence chain.

Abstract Class
–contain both abstract methods as well as concrete methods
–can extend another class and implement multiple interfaces
–we can’t achieve multiple inheritance
–allows accessibility modifiers
–can contain fields, constructors
–class Abstract class is must inheritable & its scope is upto derived class


Problem: You have a table (table1) & values as above, and it contains the duplicate records as shown, how will you delete the duplicates?


Solution: Use following query, the records shown in the below image will be deleted

delete from table1 where empid not in
(select max(empid) from table1 group by empName,empEmail,empCity);