As the world becomes more data-driven, SQL is increasingly moving from a “nice to have” skill to a first class requirement for disciplines like Data Science, Machine Learning and Business Intelligence. Here’s a free resource for learning SQL right in your browser.
With the fight between Python and Java on which will rank top of the TIOBE index, it is easy to forget that are other contenders filling the top 10. And one of those is SQL, moving up into 10th place this July, as reported in “Python Trending To Top Spot In TIOBE Index“.
SQL used to be considered an important but secondary skill that complemented the prime skill of knowing a true programming language like Java. That is, until recently, you could get a job that required Java and not SQL, but not the other way around. Possessing both of them was ideal and that would be reflect in the salary as well. But, as HackerRank’s recent University Recruitment report emphasizes, knowing SQL as well as Java or Python is an increasingly recognized as essential by both job seekers and hiring managers.
SQL has certainly proved very resilient in time, currently spanning several decades since its inception. Inherent value aside,that it remained ever relevant has to also do with its continuous revamps in the form of the ongoing ANSI SQL standards which are refreshing the language. This demonstrates to the cool kids that a technology being old doesn’t also mean that it is irrelevant.
With that in mind, resources for educating oneself in the language have been on the rise. One of those worth mentioning is SQLBolt. It is free and interactive as all code exercises run inside the the browser; no DBMS and Database with data to setup.
It is addressed to total newbies to the language so it starts off with a very small introduction to what a relational database is before tackling the SQL syntax.The actual lessons begin with “SELECT queries 101” which includes the following passage:
To retrieve data from a SQL database, we need to write SELECT statements, which are often colloquially referred to as queries. A query in itself is just a statement which declares what data we are looking for, where to find it in the database, and optionally, how to transform it before it is returned. It has a specific syntax though, which is what we are going to learn in the following exercises.
quoted here to indicate the target group the course has been designed for.
After showcasing the SELECT syntax it’s practice time. You must do an interactive exercise, in this case writing a query to find:
- the title of each film
- the director of each film
- the title and director of each film
- the title and year of each film
- all the information about each film
from a Movies table.
The nice thing about it is that as soon as you amend the query, you also are presented with the results of its run without further action. If you can’t solve them, fear not as at a side panel available on demand contains the solutions for each task at hand. Note that each lesson is like that. It first introduces a concept and ends up with an interactive exercise.
The full list of the lessons included is :
Introduction to SQL
SQL Lesson 1: SELECT queries 101
SQL Lesson 2: Queries with constraints (Pt. 1)
SQL Lesson 3: Queries with constraints (Pt. 2)
SQL Lesson 4: Filtering and sorting Query results
SQL Review: Simple SELECT Queries
SQL Lesson 6: Multi-table queries with JOINs
SQL Lesson 7: OUTER JOINs
SQL Lesson 8: A short note on NULLs
SQL Lesson 9: Queries with expressions
SQL Lesson 10: Queries with aggregates (Pt. 1)
SQL Lesson 11: Queries with aggregates (Pt. 2)
SQL Lesson 12: Order of execution of a Query
SQL Lesson 13: Inserting rows
SQL Lesson 14: Updating rows
SQL Lesson 15: Deleting rows
SQL Lesson 16: Creating tables
SQL Lesson 17: Altering tables
SQL Lesson 18: Dropping tables
SQL Lesson X: To infinity and beyond!
It’s important to note that as the lessons move on, they cover more advanced syntax. For example, in SQL Lesson 4: Filtering and sorting Query results, we get to fiddle with LIMT and OFFSET:
SELECT title FROM movies
ORDER BY title ASC
LIMIT 5 OFFSET 5;
The more advanced topics, which also apply the finishing touch to the course, occupy a distinct section, Additional Topics:
- Intermediate SQL Topics
- SQL Topic: Subqueries
- SQL Topic: Unions, Intersections & Exceptions
All in all the material is nicely presented in an easy-to-understand way. It also proves pretty comprehensive for an introduction – it’s all there: inner joins, outer joins, aggregates, offsets, NULLs and some DDL.
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