What is indexing? (Including how it works and tips)

By Indeed Editorial Team

Updated 23 November 2022

Published 4 May 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Indexing is an SQL database term that refers to the organisation of different data entries. It can help whoever is using a database to find information much faster and increase their productivity levels at work. If you work in a role that involves using databases, you could benefit from learning the answer to 'What is indexing?'. In this article, we look at what indexing is, how it works and tips for creating an effective database index.

What is indexing?

Knowing the answer to 'What is indexing?' can be beneficial if you frequently work with databases. Indexing is a process used within databases and it generally refers to the ordering of information. It's a way of providing some order to an unordered table, which allows an employee to search for certain information within the database more efficiently.

Normally, when a user enters a query, the query searches through each row linearly, checking whether it contains the information required. With an index, this process is much more streamlined and this allows the user to get through their workload faster, which increases their productivity.

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How does an index work?

Rather than reordering the database each time an employee enters a query, an index works much more efficiently than this. Instead, the index creates its own structure within the database. For example, a database may use a B-Tree format. This structure is a self-balancing one, meaning that it's able to maintain the data that's initially inputted, while also allowing for additional insertions, deletions, searches and sequential access. It also allows for nodes that have two or more branches, allowing an employee to generalise their binary searches. This has many organisational advantages for use in the workplace.

Example: A receptionist working within a GP surgery uses a database with a B-Tree format to acquire patient data. This database successfully retains patient records, but it also allows the receptionist to add and delete information, so they can take out an old telephone number and add in a new one without amending any other data. In the future, if the receptionist wanted to find out the identity of a caller, they can run the phone number through the search tool, which then returns information about the patient.

Related: What is a database query? (Plus methods and types)

Tips for creating a database index

Below, you can find some tips that can help you create an effective database index:

Index according to workload

To create an effective database index, you can create one according to your workload. Rather than starting the process of creating a database index based on the number of tables that you have, which can be harder to access, try to create an index that allows the database user to search for a particular term.

Example: A teacher creates a database index that allows them to search for pupils via their name. This is more efficient as numbers can fluctuate throughout the year as new pupils start and current pupils leave. By searching for just the name, the teacher can bring up the pupil's contact information.

Use predicates

Using predicates is another way to create an effective database index. A predicate is a type of condition expression, which is typically used to evaluate whether a fact is true or false. This also streamlines the creation of an index as it can enable the user to make a solid decision on the types of information to retrieve.

Example: A database created for the construction industry may use predicates in its index, which allows the user to search for the materials to use on a job. It might be that an employee uses it to check whether it's true that certain materials were previously used on a similar project months ago.

Index the most heavily used queries

For maximum efficiency, an index is also often built with regards to the SQL queries that most people are going to search for. This may include a list of the different SQL queries with estimations of how often an employee is going to use it, with the most important ones highlighted.

Example: A school may find this useful when they want to complete a common database search, such as when they want to determine which students have received the most calls from home or have an ongoing illness. This proves useful in an emergency as it makes their parents' details much faster and easier to find.

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Create an index that avoids sorting

One way of decreasing the time it takes for a query to find the necessary information is to create an index that avoids sorting. Often, a database user can use the 'Group by' and 'Order by' clauses to sort the records manually. To improve the performance of the database, you can create an index that's based on the columns that these two sorting functions relate to. Queries are then more optimised as there's no requirement to sort through the records.

Create unique indexes

When creating an efficient database, an employee is often required to create a series of unique indexes. This is important as it ensures that there aren't identical values found within different columns, which maintains the integrity of the data inside. Most database systems that have unique indexes create them through the use of constraints, which refers to the rules that the data in the table are always required to follow. They also use a primary key, which helps to identify the information found within a table.

Consider foreign keys

Creating indexes that relate to each foreign key featured within the database can help an employee to optimise the performance of their database as well. A foreign key is a set of columns that link to tables featured inside other databases. Although most database systems aren't typically required to use these types of indexes, they can help to improve employee performance. For example, an employee may search for a piece of data that isn't necessarily in the database, though this key can help the employee to find the right result within another database.

Add columns for index-only access

In some cases, it's beneficial for an employee to include a series of additional columns into their database that have index-only access. This allows an employee to access index-only data more quickly. The reason behind this is that when the user enters a query, it only has to find the data inside these added index columns. This gives an employee the exact information requested in a faster time. But, it's important to note that the employee is now required to examine the other queries to determine whether the additional columns are going to impact how they can function.

Avoid a limit on the number of indexes

When creating indexes for a database, it's important to avoid limiting the number of indexes that you have. An index is an optimiser that allows an employee to access data faster, so it's beneficial to have as many as possible to fully optimise a database. It's important to note that this doesn't only benefit one employee, as colleagues typically share databases and the information that's contained within them. This means that it can increase the productivity of an entire department when completing a task.

Check to see if there are many data modification implications

An employee may find it useful to avoid the data inputting stage as this can be time-consuming. They can do this by considering the implications surrounding data modifications. There are a few ways to do this. For instance, an employee can examine the indexes that are on the table. If there are more indexes than columns, there's a good chance that adding another index doesn't usually have a big impact on performance. An employee can also run a query against the table to see how long it takes to execute. If the query doesn't take a long time to run, it's worth adding an index.

In addition, an employee that wants to add or delete pieces of data so that they can create their own indexes could examine how this action is going to affect the rest of the table first. For example, if the database is full of contact details for vendors, it's unwise to get rid of telephone numbers that direct the organisation to a specific employee.

Disclaimer: The model shown is for illustration purposes only, and may require additional formatting to meet accepted standards.

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