Emprotek Software Solutions Interview Questions and Answers

A class is a blueprint or template for creating objects, while an object is an instance of a class.

• A class defines the properties and methods that an object will have.

• An object is created from a class using the 'new' keyword.

• Multiple objects can be created from a single class.

• Objects can have different values for their properties, while the class defines the structure.

• Classes can inherit properties and methods from other classes, while objects cannot.

A primary key is a unique identifier for a record in a database table.

• It must be unique for each record in the table

• It cannot be null or empty

• It is used to establish relationships between tables

• Examples: social security number, email address, student ID

A foreign key is a column or set of columns in a table that refers to the primary key of another table.

• It establishes a relationship between two tables.

• It ensures referential integrity.

• It can be used to join tables in a query.

• Example: CustomerID in Orders table refers to the CustomerID in Customers table.

A unique key is a field or combination of fields that uniquely identifies a record in a database table.

• A unique key ensures that no two records in a table have the same values for the key fields.

• It can be a single field or a combination of fields.

• It is used to enforce data integrity and to facilitate efficient data retrieval.

• Examples include primary keys, candidate keys, and alternate keys.