How does indexing improve the efficiency of database queries?

Indexing improves the efficiency of database queries by providing quick direct access to rows in a database table.

In more detail, an index in a database is similar to an index in a book. It is a data structure that improves the speed of data retrieval operations on a database table. Without an index, the database server must begin with the first row and then read through the entire table to find the relevant rows. This is called a table scan, and it's a very slow way to retrieve data. However, if an index has been defined, the database server can use it to find the required rows more quickly and efficiently.

Indexes are used to quickly locate data without having to search every row in a database table every time a database table is accessed. They can be created using one or more columns of a database table, providing the basis for both rapid random lookups and efficient access of ordered records.

The process of creating an index involves the database management system (DBMS) creating a new data structure that holds the indexed field value, and a pointer to the record that the field value belongs to. This indexed data structure is then sorted, allowing Binary Search to be used on it. The sorting enables the DBMS to find the pointer to a record with a particular field value more quickly, as it doesn't have to scan the whole table, just the index.

However, it's important to note that while indexes speed up data retrieval, they slow down data modification operations such as insert, update and delete. This is because every time data is changed, the index must be updated as well. Therefore, the decision to index a particular table or column should be made carefully, considering the nature of the data and its usage.

In conclusion, indexing is a crucial aspect of database management that can greatly improve the efficiency of data retrieval, but it must be used judiciously to avoid slowing down data modification operations.