Joining Data Using SQL

Name: Joining Data Using SQL
Author: Eric Grose

Understand how and when to join data using SQL

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Course: On-Demand

Hello, my name is Eric, and in these lessons, you'll learn about joining data in SQL. In this lesson, I'll show you the fundamentals of the join command in SQL. Join is a way to combine data from two or more tables in a database. Joins are used to retrieve data from multiple data tables based on a common column between the two tables. There are several different types of joins being the interjoin, outer join, left join, and cross join. To create a join in SQL, we'll use the join keyword followed by what type of join we want to use and the tables we want to join together. Also, we'll be adding the on clause which specifies the join condition or how the rows from the two tables are matched. So, let's take a look at the syntax here. We're just going to select all columns by doing Select Star, we say from table one, specify what type of join we want to do with table two, and our on clause is where we define the two columns that are matching between the two tables. If you have a common column between two tables, you can join them together for a much richer data set and for much richer insights. Now, you can also use the using clause to specify join condition, but it only allows you to specify a single column name instead of a full expression. If we wanted to here, we could add multiple on clauses. If they matched between the two tables, it would make our query much more performant, so using the using command makes it much easier to write, but less performant in the long run. Using this syntax here, we're going to select all columns again from table one, specify what type of join with table two, and then all we have to do is the using command and the column name that is matching between the two tables. You can also join multiple tables by chaining multiple join clauses together. For example, in this syntax here, we're going to select all the columns, again from table one, again, specify what type of join from table two, we'll have the same type of on clause where we define how the two tables are matched based on a light column, and then from there, we just specify the next join, what type of join is it in our table three, and then another on clause where the columns match between two tables. The more tables you're able to join, in general, the more context you're able to provide to your analysis and obtaining much richer insights. Stay tuned to the next lesson where I show you inner joins in SQL. Thanks for watching.

Intermediate Provider : Eric Grose 3 Lessons · 6m in English

Course Description

Joining data tables is the truest and most impactful way to perform data analysis using SQL, since learning the commands for this operation will allow you to combine data from multiple sources. Generally speaking, the more data you can add to your analysis, the more insights you will be able to determine.

However, just adding data for the sake of adding data can result in slow performing queries that bog down a system and will put you on the fast track to disciplinary action as an analyst. In these lessons, we’ll cover when it’s appropriate to join data tables together, as well as the different types of join an analyst can perform. Being able to construct performant join queries is a practice that will dramatically improve your skills and abilities as an analyst, and by the end of these lessons, you’ll know the techniques for navigating any database and combining any available tables into your analysis.

What You'll Learn

Understand the principles of joining data using SQL and when it is appropriate to do so
Recognize the scenarios where an inner join fits the data you are analyzing
Identify opportunities to perform an outer join for data analysis
Apply join fundamentals to combine data from multiple sources
Construct performant join queries that avoid bogging down a system

Key Takeaways

Joining data tables lets you combine data from multiple sources, which is the truest and most impactful way to perform data analysis using SQL.
Adding more data to your analysis generally allows you to determine more insights.
Adding data without purpose can result in slow performing queries that bog down a system.
The course covers when it is appropriate to join data tables together and the different types of join an analyst can perform.
Being able to construct performant join queries dramatically improves your skills and abilities as an analyst.

Frequently Asked Questions

What will this course teach me about SQL joins?

It covers when it is appropriate to join data tables together and the different types of join an analyst can perform, including inner joins and outer joins, so you can combine available tables into your analysis.

What topics are covered in the lessons?

The lessons cover Join Fundamentals, Inner Joins, and Outer Joins.

Why does query performance matter in this course?

Adding data just for the sake of it can result in slow performing queries that bog down a system, so the course teaches how to construct performant join queries.

What skills will I build?

You will build skills in Data Analysis, Data Integration, Data Manipulation, Data Modeling, Database Analysis, and SQL.