How to Learn SQL

SQL is a critical skill for anyone working with data and it is essential for anyone interested in a career in data analysis, data science, or business intelligence. Learning SQL can be challenging, but with the right resources and approach, it can also be incredibly rewarding.

So, this article is a beginner’s guide to learning SQL, including everything to start growing your data analysis skills.

What is SQL and why you need it

SQL, or Structured Query Language, is a powerful programming language used to store and manage data. It is used by data analysts, database administrators, and business intelligence professionals to store, update, and analyze data stored in relational databases like MySQL or Postgres.

SQL is quite a universal skill if you work in data-related field such as finance, healthcare, marketing, etc. But it’s a mandatory skill for data analysts and data scientists to be able to organize the data and the data for further analysis. Being able to use SQL, you can analyze customer data insights, company’s financial flows, products, and answer any question based on business-related data.

SQL concepts you will need to learn

SQL basics

Here are 3 of the most basic concepts of SQL:

  1. SQL tables are the fundamental structure in a relational database, consisting of rows (or records) and columns (or fields). Rows represent individual entries in the table, while columns represent the attributes or characteristics of those entries. For instance, you might have a table “Customers” where columns will include the same attributes like age or location, while rows will represent each customer (age and location of a specific customer).
  2. SQL queries are pieces of text (code) used to retrieve or organize data stored in a database. Queries can be used to filter, aggregate data, perform calculations, and create new tables.
  3. SQL syntax is a set of rules or commands for writing universal SQL queries that will work in any environment. Basic SQL commands include SELECT, FROM, WHERE, INSERT INTO, UPDATE, and DELETE, among others.

Main SQL operations

  • Creating Tables: To create a new table in SQL, you need to specify the name of the table, the columns it will have, and their data types. You can also define primary and foreign keys, constraints, and other table properties.
  • Inserting Data: Once you have created a table, you can insert data into it using the INSERT INTO command. You specify the name of the table and the values to be inserted into each column.
  • Updating Data: You can modify existing data in a table using the UPDATE command. You specify the name of the table, the columns to be updated, and the new values. You can also use the WHERE clause to update specific rows that meet certain criteria.
  • Deleting Data: You can delete data from a table using the DELETE command. You specify the name of the table and the rows to be deleted using the WHERE clause.
  • Selecting Data: The SELECT command is used to retrieve data from one or more tables in a database. You can specify which columns to select, filter the data using the WHERE clause, and sort and group the results using the ORDER BY and GROUP BY clauses.

Advanced SQL functions

  • Joining Tables: When working with multiple tables in a database, you may need to combine data from two or more tables. This can be done using SQL joins, which allow you to match rows from one table with rows from another based on a common column. Common types of joins include inner joins, outer joins, and cross joins.
  • Aggregating Data: SQL provides several functions for aggregating data, such as SUM, COUNT, AVG, MIN, and MAX. These functions allow you to perform calculations on groups of data, such as finding the total sales for a particular product or the average salary of employees in a department.
  • Grouping Data: The GROUP BY clause is used to group rows in a table based on one or more columns. This allows you to aggregate data and perform calculations on subsets of data within a table.
  • Filtering Data: The WHERE clause is used to filter data based on specific criteria. However, SQL also provides additional filtering options, such as the HAVING clause, which is used to filter data based on aggregated values, and the LIKE operator, which allows you to search for patterns in text data.

Here is a list of the most common SQL functions, according to W3schools:

Tips to get started with learning SQL

The first tip is to spend a lot of time to get used to SQL syntax. It’s same as with any language: to be able to use it, you first need to know its rules. Thankfully, SQL is pretty easy language and usually you will use the limited number of its functions. Start by going through a lot of queries including functions like Count, Distinct, Min/Max/Avg, Order BY or Group By.

Another tip is to focus on answering questions rather than simply write an SQL statement. As a data analyst your main role is to answer business-related questions with data. So, first list the questions to answer and then, find the most effective way to do this with SQL. For instance, instead of stating tasks like “I need to write an SQL using Max“, ask questions like “What is the lowest price of our products.” You got the idea.

Finally, join at least one SQL community to get advice on your task, understand struggles of others while learning SQL, or find new SQL-related tasks for yourself. This can be some Slack communities and they are good way to continue learning SQL. You can also get a career-related advice there and understand common use cases of SQL by people who already use SQL for their work.

Courses and resources to learn SQL

Here the website that will help you to progress in your learning.

  • Learn SQL by Codecademy is a free course that covers the main basic concepts of SQL. It’s an 8-hour course covering basic topics how to create and update tables and also questions of more complex SQL quesries.
  • SQL Fundamentals by DataCamp is a set of 5 single courses to fully understand SQL. The course takes 21 hours to complete and includes both beginner and intermediate topics like how to filter, compare, sort and group data, join table,s and many others.
  • SQL Tutorial by W3schools is a useful source to learn basic concepts and practice using them. While this tutorial is not comprehensive as the two previous once, it’s completely free and easy to follow.
  • SQL Tutorial by freeCodeCamp is a 4-hour engaging Youtube tutorial coving everything you need to know about SQL. Don’t forget to have enough hand-on practice during and after watching the vide.
  • SQL for Data Science by Coursera is another course that will be the most useful for understanding how data scientists use SQL and what SQL skills you need to learn working in this field.

In conclusion, SQL is a critical skill for anyone working with data. Whether you are just starting out or looking to enhance your skills, learning SQL can be a challenging but rewarding process. By following these tips, you can become proficient in using SQL to manage and manipulate data stored in relational databases. With SQL, you can gain insights, make informed decisions, and communicate your findings in a way that is both meaningful and impactful.

Stacey M.
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