Introduction to indexes and constraints
An index is a pointer to the actual rows in its corresponding table. It is used to find and retrieve particular rows much faster than using the standard method. Indexes help you improve the performance of queries. However, indexes get updated on every Data Manipulation Language (DML)—that is, INSERT, UPDATE, and DELETE—query on the table, which is an overhead, so they should be used carefully. Constraints are basically rules restricting the values allowed in the columns and they define certain properties that data in a database must comply with. The purpose of constraints is to maintain the integrity of data in the database. The different ways of maintaining data integrity through constraints will be covered in this chapter.
Primary key indexes
As the name indicates, primary key indexes are the primary way to identify a record (tuple) in a table. Obviously, it cannot be null because a null (unknown) value cannot be used to identify a record. So, all...
