Gain insights into SQL by exploring database creation, data manipulation, and advanced queries. Learn about practical applications and practice for SQL interviews to build confidence and readiness.

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The ability to work SQL is becoming an increasingly in-demand skill, both for software developers and people in less technical roles. If you’re interested in learning SQL and have no prior experience with it, then this course will be your light in a dark tunnel.

You’ll start by covering the basics of SQL such as how to create a database, how to insert, query, and update data. You’ll also learn fundamental concepts that developers and data scientists use everyday such as multi-table operations, nested queries, and how to set up views. 

Throughout, you’ll get to execute SQL queries in your browser and see results in real-time - you won’t need to worry about set-up.

At the end of this course, you’ll also get some hands-on practice with common SQL interview questions, so when the time comes, you’ll be ready and confident to answer any question that comes your way. Let’s get started!

An Introductory Guide to SQL

# Foreign Keys

In this lesson, we'll discuss foreign keys. Not all storage engines support foreign keys. In MySQL, InnoDB supports foreign keys but MyISAM doesn't. Let's try to understand the concept through the example we have been working on in this course. The __DigitalAssets__ table consists of online accounts for actors in our __Actors__ table. The two tables are related to each other by the columns ID and ActorID. Logically, it doesn't make sense to have a row in the __DigitalAssets__ table for an actor who is not listed in our __Actors__ table. Ideally, we would want that anytime we add a new row to the __DigitalAssets__ table a corresponding entry in the __Actors__ table exists with the same ID as the ActorID of the new row being added to the __DigitalAssets__ table. Similarly, if we delete any actor from the __Actors__ table we'd want all rows in the __DigitalAssets__ table associated with the actor to be deleted too.  We can enforce these restrictions using the foreign key constraint.

The relation between the two tables is one to many. A foreign key can be a column or a group of columns in a table that link to a column or a group of columns in another table. In this case, the __Actors__ table is the referenced table and called the parent table, whereas, the referencing table __DigitalAssets__ is called the child table.


## Example Syntax
> CREATE TABLE childTable (
>
> col1 **\<dataType>**,
>
> col2 **\<dataType>**,
>
> CONSTRAINT **fkConstraint**
>
> FOREIGN KEY **(col2)** 
>
> REFERENCES **parentTable(referencedCol)**;
> 
>


>Connect to the terminal below by clicking in the widget. Once connected, the command line prompt will show up. Enter or copy and paste the command **./DataJek/Lessons/41lesson.sh** and wait for the MySQL prompt to start-up.

Introduction

Basic SQL

Joins

Nested Queries

Multi Table Operations

Views

Stored Procedures

Triggers

Miscellaneous

Practice & Prep

Epilogue

Foreign Keys

Foreign Keys