The purpose of Views and Indexes.

Full Answer Section

• SQL

  CREATE VIEW CustomerOrders AS
  SELECT c.CustomerID, c.Name, o.OrderID, o.OrderDate
  FROM Customers c
  JOIN Orders o ON c.CustomerID = o.CustomerID;
  

  Now, you can simply query the CustomerOrders view as if it were a table: SELECT * FROM CustomerOrders;

• Why use a view?

  • Simplification: Hides the complexity of underlying queries, making it easier for users to access data.
  • Security: Restricts access to specific columns or rows. You can grant users access to a view that only shows the data they need, without giving them access to the underlying tables.
  • Data Independence: If the structure of the underlying tables changes, you can modify the view definition to maintain the same interface for users, minimizing the impact of database changes.

Indexes:

• Purpose: An index is a data structure that improves the speed of data retrieval. It's similar to an index in a book. Instead of scanning the entire table, the database can use the index to quickly locate the rows that match the query criteria.

• Example: In the Customers table, if you frequently search for customers by their LastName, you can create an index on the LastName column:

  SQL

  CREATE INDEX idx_lastname ON Customers (LastName);
  

  When you execute a query like SELECT * FROM Customers WHERE LastName = 'Smith';, the database will use the idx_lastname index to quickly find the rows where LastName is 'Smith', rather than scanning the entire Customers table.

• Why use an index?

  • Performance: Significantly speeds up data retrieval, especially for large tables.
  • Efficiency: Reduces the amount of work the database server needs to do, improving overall database performance.

Key Differences and When to Use Which:

• Views: For simplifying complex queries, restricting data access, and providing data independence. They don't store data independently.
• Indexes: For improving the speed of data retrieval. They are a separate structure that helps quickly locate data within tables.

In short, views are about how you see the data, while indexes are about how quickly you can find the data. They often work together. You might create a view to simplify a complex query and then create an index on the underlying tables (or the view itself, in some databases) to speed up the retrieval of the data shown by the view

Sample Answer

Views and indexes are database objects that serve distinct purposes to improve data access and management.

Views:

• Purpose: A view is a virtual table based on the result-set of an SQL statement. It's like a saved query. It doesn't store data itself; instead, it retrieves data from the underlying tables whenever it's queried. Views simplify complex queries, restrict data access, and provide a layer of abstraction between the user and the actual database schema.

• Example: Imagine you have a database with tables Customers and Orders. You frequently need to see a combined view of customer name, order ID, and order date. Instead of writing a complex JOIN query every time, you can create a view: