18 Useful Important SQL Functions to Learn ASAP

Updated on: October 30th, 2023

Learning a new programming language can seem intimidating. Like any other language, a programming language has a large vocabulary that you need to master. In this article, we’ll look at some of the most useful SQL functions that you need to know.

Structured Query Language, commonly known as SQL, is the standard language for managing and querying data in relational databases. Born out of the need to efficiently interact with large datasets, SQL has become an indispensable tool for database administrators, data analysts, and developers alike. Its syntax allows users to retrieve, insert, update, and delete data, making it the backbone of many modern software applications and data-driven decisions.

Over the years, SQL has evolved and been adapted by various database systems, leading to slight variations in its implementation. However, its core principles remain consistent, ensuring that skills learned on one platform can often be transferred to another. Whether you're running complex analytical queries or simply pulling up customer information, SQL provides a robust and efficient means to communicate with databases.

In this article, we'll guide you through some of the most useful SQL functions that every data enthusiast should be familiar with. These functions are the building blocks for effective database querying and management.

If you're just starting out or looking to solidify your foundational knowledge, we highly recommend our SQL Basics course. It's one of the best interactive online courses available, designed to equip you with the essential skills needed to navigate the world of SQL with confidence.

Beginning with SQL: Useful Functions to Master

As you dive into the vast world of SQL, you'll quickly discover a plethora of functions tailored to manipulate and analyze data. These functions, designed for various data types, are your essential tools for crafting powerful queries. Whether you're working with strings, numbers, dates, or other data types, there's a function waiting to simplify your task.

By dedicating time to practice, you'll soon master these foundational functions, setting the stage for more advanced SQL challenges. As you progress, you'll find that these functions not only elevate your querying skills but also boost your confidence in tackling intricate datasets. So, are you ready? Let's dive in and uncover some of the most crucial SQL functions that you should add to your toolkit.

1. String Functions

A string is just a series of one or more characters that have been strung together. Quite simply, string functions deal with strings!

Length

The simplest SQL string function is length. As its name suggests, length returns the number of characters that a given string contains (including spaces and punctuation). Let's look at a simple PostgreSQL select statement and feed it with the string 'Hello, my name is':

select length('Hello, my name is');

The result of running this query is 17. If you manually count the number of characters (including spaces) in the above string, you'll find that 17 is a precise match! While length may at first seem like a trivial function, you will actually use it very frequently.

Trim

Let's trim some fat! Another example from the most useful SQL functions category is trim. It eliminates excess spaces and tabs from the beginning and end of a string that we pass in as its argument. For instance, if we pass in the string ' Hello, my name is ', we will receive the same string but without all those leading and trailing spaces. Here's a basic query with that string:

select length('  Hello, my name is  ');

As expected, the above query returns 'Hello, my name is'.

Concat

The concat function combines (concatenates) two or more strings that we pass in as its arguments. Here's an example of string concatenation in action:

select concat(' Hello, ', 'my name is ', 'Paul');

This query returns the string 'Hello, my name is Paul'.

Upper

Given a string, upper returns the same string but with all its characters cast to uppercase. So, if you'd like everyone to hear you loud and clear, you can write the following query:

select upper('Hello, my name is Paul');

This returns the string 'HELLO, MY NAME IS PAUL'.

Lower

The function lower is the direct opposite of upper — it takes a string and returns the same string with all its characters cast to lowercase. Here's a query that uses lower:

select lower('Hello, my name is Paul');

Predictably, we get the string 'hello, my name is paul'.

Initcap

This function capitalizes the first (initial) letter of each word in a given string. For example, you can use initcap to ensure that the name someone has provided adheres to proper capitalization rules. Here's an example of the function in use:

select initcap('paul anderson');

The result of the above query is 'Paul Anderson'.

Of course, there are many other useful SQL functions used for strings, like replace, substr, and others. To learn more about these, check out LearnSQL.com's Standard SQL Functions interactive course! Thanks to it, you'll learn about the other common SQL functions I didn't mention in this article.

2. Numerical Functions

Numerical functions simply work with numbers, and there are quite a lot of useful SQL functions in this category. Let's discuss a few of these.

Abs

Trimming? Abs? Yeah, I know what you're thinking, but this isn't a workout program. Abs is shorthand for absolute; it's one of the most common SQL functions. It calculates the absolute value of a numeric value we pass in as its argument. In other words, abs returns the positive version of a given number. Here's an example:

select abs(-22),abs(22);

If you've been paying attention in math class, you'll know that both of these calls to abs return the number 22.

Round

The round function takes a floating-point (decimal) number rounds it to the nearest integer. Take a look at this simple example:

select round(5.4),round(5.5),round(5.6);

We would get 5 (next smallest integer), 6 (next largest integer), and 6 (next largest integer), respectively, for the above three calls to round.

Ceil

The ceil function returns the ceiling of a number—the first integer greater than or equal to that number. To visualize this process, place the number in question (say -0.5) on a standard number line and move right, towards the next largest integer (in this case, that's 0). Here's an additional example:

select ceil(5.4),ceil(5.5),ceil(6);

We receive the numbers 6, 6, and 6 for these three calls.

Floor

Floor is the reverse of the ceil function; it returns the floor of the decimal number we pass in as its argument — the first integer that is less than or equal to that number. For example, the floor of -0.5 is -1, as that is the first integer that is less than -0.5. With the number line visualization, you start at the given number and move left towards the next lowest integer. If we repeat the above calls with the floor function:

select floor(5.4),floor(5.5),floor(6);

We receive three numbers: 5, 5, and 6.

Sign

One of the simpler functions on this list, sign takes a number as its argument and returns -1 if the number is negative, 0 if the number is 0, and 1 if the number is positive. It's as easy as that! Here's an example:

select sign(-5),sign(0),sign(5);

This query returns the following numbers: -1, 0, and 1.

Mod

Mod stands for modulo. It is a very powerful SQL function that returns the remainder of the first argument divided by the second argument. For example, dividing 5 by 2 results in a remainder of 1. Thus, the function call mod(5, 2) returns the number 1.

The modulo operator has many useful applications, and one of its common uses is determining whether a given number is even or odd. If a number is even, the remainder of dividing that number by 2 is 0. Otherwise, the remainder is 1. Thus, given a number n, you can use mod(n, 2) to determine whether n is even or odd!

There are many more useful SQL functions in the numerical category you should know, such as trunc, trigonometric, logarithmic, power, root, and more. The best place to master these is LearnSQL.com's Standard SQL Functions course. If you haven't already, go ahead and check it out!

3. Date Functions

As this category's name suggests, date functions work with dates! In this section, we'll take a look at some of the most useful SQL functions of this type.

Current_date

First on our list is current_date, an extremely useful SQL function that … returns the current date! Here's an example query:

select current_date;

For us, this will return 2023-10-29.

Extract

This common SQL function allows you to extract certain parts of a date (such as the day, month, or year) that you pass in as an argument. Here's an example of all three uses:

select extract(day from date'2017-1-1'),extract(month from date'2017-1-1'),extract(year from date'2017-1-1');

The above query returns the following three numbers: 1, 1, and 2017.

Date_trunc

The date_trunc function truncates the values of a given date to a specific granularity. Let's say you have a date, but you want to have only the first day of the month of that date. To do this you would truncate the date value to the 'month' parameter. Let's look at an example:

select date_trunc('month',date'2017-4-2') 

This would return the date of 04-01-2017. If we would feed the year value as a granularity:

select date_trunc('year',date'2017-4-2')

We would receive the first day of the inputted year, 01-01-2017.

4. Miscellaneous Functions

In addition to the functions we've covered so far, there are a couple miscellaneous functions that are commonly used in SQL programming.

Coalesce

Sometimes, you'll come across null values when working with tabular data. These represent absent or missing information. Unfortunately, any calculation involving a null value will return null, and this is not always ideal.

The COALESCE function takes a list of arguments and returns the first of these that does not contain a value of null. In other words, if SQL finds that the first argument you provided is null, it will move on to evaluate the second argument, repeating the process until it either finds one that isn't null or simply runs out of arguments.

For example, suppose we're working with a table that has a numeric column named potentially_null_column. Let's say this column has several values—some that are null and others that are not. Suppose we execute the following code:

select COALESCE(potentially_null_column, 0);

Here, the query will use a value of 0 whenever a cell in the potentially_null_column stores a value of null. For cells in that column that are not null, the query will simply use their values. This SQL function is most useful in calculations involving columns that may contain null values, as it prevents unexpected behavior. To learn more about COALESCE and its uses, check out this article.

Greatest

Another very useful SQL function, greatest takes a list of expressions and returns the largest of them. Here's an example of it being used:

select greatest(1,2,3,5,6);

Naturally, this query returns 6, as that is the greatest value in the list we provided.

Least

least is the direct inverse of greatest. If we write the following query:

select least(1,2,3,5,6);

it returns 1, as that is the smallest value in the list we provided.

And Once You Know These Useful SQL Functions...

There is a variety of useful SQL functions for manipulating strings, numbers, dates, and other data types. Now that you've learned a bit about the basics, you should consider delving deeper into these subjects to expand on what you already know.

For that, there's simply no better place to start than LearnSQL.com! Starting your SQL journey? Dive into LearnSQL.com's SQL Basics course. It's tailored for beginners, covering the essentials from crafting basic queries to understanding data relationships. It’s a perfect foundation for your SQL adventure. You can try the first few exercises without any cost. Just create a free account –- no credit card required! All our interactive SQL courses run directly in your browser. No installations are needed.

If you're a more seasoned SQL user, elevate your skills by diving into our Advanced SQL Track, which includes:

1. Standard SQL Functions – In this course you'll learn how to process numerical, text, and other types of data with the most useful SQL functions.
2. Window Functions course – Here you’ll learn window functions also known as analytic SQL functions.
3. Recursive Queries – In this course you’ll learn how to process trees and graphs in SQL, and how to effectively organize long SQL queries and subqueries.

You can also find out about different ways to practice advanced SQL with our platform.

You've already learned the most common SQL functions. Now, take your self-development to the next level and master the most challenging SQL queries!