How To

Dorota Wdzięczna

SQL Cookbook with Recipes for Success

The internet holds a lot of information and can provide solutions to various problems. SQL users, both beginners and advanced, often turn to the internet for help with SQL queries. This article will help you find the right SQL queries to solve your problems. Learn what the SQL Cookbook is and why you should use it. You will also find a list of the most important recipes, from which you will prepare a great SQL dish with the taste of success.

LearnSQL.com Team

Practical Ways to Improve the Performance of SQL Queries

Knowing how to improve SQL query performance is an important skill, especially when working with with large databases. In this article, you'll learn how to write more efficient SQL queries to get results faster. The biggest difference between SQL and other languages is that SQL is a non-procedural language. In a non-procedural language you specify the results that you need but not the methods used to get it. The advantage of a non-procedural language is that it is easier to write programs, therefore it is common for non-programmer business users to generate reports from SQL queries.

Ignacio L. Bisso

How to Begin Running SQL Queries

In this article, I’ll explain how to run a SQL query to help you execute your first one. Let’s jump right in! Running SQL queries for the first time is not a complex task, but it can seem intimidating at first if you’re a complete beginner. But once you get past that initial roadblock, you’ll be able to focus on learning SQL and writing more interesting queries to meet your business needs.

Aldo Zelen

How to Use a SQL Wildcard

SQL wildcard allows us to filter data matching certain patterns in SQL. We use SQL wildcards with the LIKE operator in the WHERE clause of a query to filter data. In this beginner’s article, we’ll look at everything you need to know about basic SQL wildcards. If you like playing cards, then you know that wildcards can substitute any other card in your deck. Similarly, SQL wildcards can substitute one or more characters.

Aldo Zelen

SQL Filtering 101

Sometimes, SQL queries return lots of data you don't need. In this article, we'll look at a simple example of filtering SQL queries to reduce the complexity of your data. The key to learning how to filter data in SQL is understanding the very basics of Boolean algebra. That's just a fancy term mathematicians use to describe expressions involving logical values (true/false) and their associated operators (and, or, not, etc.

Ignacio L. Bisso

Improving Slow Query Performance: When Runtime Matters

As SQL users, we usually focus on writing queries that return correct results. However, there are more things to consider when you're writing a query; one of them is query performance. In this article, we'll look at some examples where query response time is critical. Scene One: 911 Call Center Let's suppose we're at a 911 call center, when the phone rings. One of the operators answers the call; a witness reports that a man has been shot.

Ignacio L. Bisso

Converting Subqueries to Joins

Not all queries are alike, especially in terms of performance. In this article, we'll look at how you can convert SQL subqueries to joins for improved efficiency. When should I use SQL subqueries? Great question! Unfortunately, there's no concrete answer. SQL beginners tend to overuse subqueries. Typically, once they find that SQL construction works in one situation, they try to apply that same approach to other situations. It's only natural.

Ignacio L. Bisso

Learn to Write a SQL Correlated Subquery in 5 Minutes

If you’re familiar with the famous Russian nesting doll, then SQL correlated subqueries should be a peace of cake to understand—subqueries are just queries nested within queries. An SQL subquery is often called an “inner” query; the main query is usually called the “outer” query. This article covers everything you need to know about correlated subqueries. What Exactly is a SQL Correlated Subquery? A correlated SQL subquery is just a subquery that is executed many times—once for each record (row) returned by the outer (main) query.

Ignacio L. Bisso

Extracting Data From a String: SPLIT_PART in PostgreSQL

Learn how to use split_part in PostgreSQL to extract data from strings. Quite often, we’d like to extract parts of a string when working with text values. A common example is when we have a full name and need to retrieve only the last name. In this article, we’ll examine how to do it using split_part in PostgreSQL, i.e. a string-related function that can be used to extract a substring.

Ignacio L. Bisso

How to Remove Junk Characters in SQL

Unwanted characters in text data can be a bit of a pain, but there’s an easy way to fix them. Scroll down to learn how to remove junk characters in SQL in the easiest way! Sometimes, we’ll find unwanted characters inside our string data because our SQL queries didn’t work as expected. Moreover, these extra characters may sometimes be invisible, which really complicates things. In this article, we’ll examine some string-related SQL functions that can handle unwanted characters—visible or not!

Ignacio L. Bisso

How to Solve Capitalization Data Quality Issues

Misspelled names, typos, and text data quality issues in your database? Power up your queries! Use SQL string functions to address data quality issues related to capitalization. Sometimes, our SQL queries don't work as expected because of data quality issues. In this article, we will examine some string-related SQL functions that can correct data quality issues related to capitalization. We'll be using PostgreSQL in our examples, but similar functions are available in most database engines.

Kacper Skawina

Analyzing Survey Data: Explore Results Using SQL

Excel is a powerful beast that lets you analyze complex data. Yet, operating on big chunks of data can sometimes be a daunting task. Let's take a look at how SQL can help. Today, we'll tackle a common problem with importing data to an SQL database, using a real-life example. Suppose your company conducted a survey on the most popular programming trends and preferences, striving to meet the expectations of its users.

Marek Pankowski

Complete SQL Practice for Interviews

Congratulations! Your SQL skills were strong enough to get you that job interview! Now, if you only knew what SQL questions and practical exercises a recruiter might ask you to do… This article is meant as a SQL practice for interviews. I’ll help you prepare for the SQL and database aspects of your job interview. In a previous article, I explained how can you boost your career by learning SQL.

Marian Dziubiak

SQL Development? Structured Query Language and Apps

You know about using SQL with databases. How does SQL fit in with app development? Is there anything like SQL development? In this post, we look at the app development process, how it intersects with modeling a database, and what developers can do with SQL outside of their app. Obviously, the beginning of this process is defining your app — what it does, who it is for, how it will function and look, etc.

LearnSQL.com Team

The Complete Beginner’s Guide to SQL Fundamentals

LearnSQL.com is a great place to learn SQL. If you’re a complete beginner, it’s best to have an overview of what SQL is, what a database is, and how they work together. In this article, you’ll find a complete guide to SQL fundamentals. SQL Fundamentals: Database Let’s begin our guide to SQL with basic definitions. You might have already heard that SQL is used with databases. What exactly is a database?

Adrian Dembek

6 Common SQL Syntax Mistakes All Learners Make

Updated on: June 22, 2024 We all make mistakes when learning a new language – especially at the beginning. New words, complicated grammar... Everyone needs time to master a language. But when we get immediate feedback, we can progress more quickly. The same goes for learning SQL. In this article, we'll look at 6 common SQL syntax mistakes most SQL learners make. Learning SQL can feel like deciphering a complex code, especially when you’re just starting out.

Marcos Pierri

8 Tips Absolute Beginners Can Use to Fix SQL Queries

Code errors are common – and frustrating. And when you're just learning SQL, it can be very challenging to find and fix your mistakes. In this post, we'll show you eight ways to solve or eliminate common SQL coding errors. Today, we'll talk about some tips the SQL beginner can use to avoid several common errors. These tips work in any database environment. As we go along, we'll be showing some error messages.

Aldo Zelen

SQL Errors: Five Common SQL Mistakes

As you learn SQL, watch out for these common coding mistakes You’ve written some SQL code and you’re ready to query your database. You input the code and …. no data is returned. Instead, you get an error message. Don’t despair! Coding errors are common in any programming language, and SQL is no exception. In this article, we’ll discuss five common mistakes people make when writing SQL. The best way to prevent mistakes in SQL is practice.

Aldo Zelen

Five Common SQL Syntax Errors

Updated on: July 19, 2024 SQL is a powerful language for managing databases, but even small syntax errors can lead to big headaches. As you work with SQL, understanding and avoiding common mistakes can save you time and frustration. In this article, we'll highlight five frequent SQL syntax errors You've written your SQL code and you're ready to query your database. You input the code, but instead of getting the data you expected, you get an error message.