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Joining Data in SQL

Join two or three tables together into one, combine tables using set theory, and work with subqueries in PostgreSQL.

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Course Description

Now that you've learned the basics of SQL in our Introduction to SQL course, it's time to supercharge your queries using joins and relational set theory. In this course, you'll learn all about the power of joining tables while exploring interesting features of countries and their cities throughout the world. You will master inner and outer joins, as well as self joins, semi joins, anti joins and cross joins—fundamental tools in any PostgreSQL wizard's toolbox. Never fear set theory again after learning all about unions, intersections, and except clauses through easy-to-understand diagrams and examples. Lastly, you'll be introduced to the challenging topic of subqueries. You will be able to visually grasp these ideas by using Venn diagrams and other linking illustrations.

  1. 1

    Introduction to joins

    Free

    In this chapter, you'll be introduced to the concept of joining tables, and will explore the different ways you can enrich your queries using inner joins and self joins. You'll also see how to use the case statement to split up a field into different categories.

    Play Chapter Now
    Introduction to INNER JOIN
    50 xp
    Inner join
    100 xp
    Inner join (2)
    100 xp
    Inner join (3)
    100 xp
    INNER JOIN via USING
    50 xp
    Review inner join using on
    50 xp
    Inner join with using
    100 xp
    Self-ish joins, just in CASE
    50 xp
    Self-join
    100 xp
    Case when and then
    100 xp
    Inner challenge
    100 xp
  2. 2

    Outer joins and cross joins

    In this chapter, you'll come to grips with different kinds of outer joins. You'll learn how to gain further insights into your data through left joins, right joins, and full joins. In addition to outer joins, you'll also work with cross joins.

    Play Chapter Now
    LEFT and RIGHT JOINs
    50 xp
    Left Join
    100 xp
    Left join (2)
    100 xp
    Left join (3)
    100 xp
    Right join
    100 xp
    FULL JOINs
    50 xp
    Full join
    100 xp
    Full join (2)
    100 xp
    Full join (3)
    100 xp
    Review outer joins
    50 xp
    CROSSing the rubicon
    50 xp
    A table of two cities
    100 xp
    Outer challenge
    100 xp
  3. 3

    Set theory clauses

    In this chapter, you'll learn more about set theory using Venn diagrams and get an introduction to union, union all, intersect, and except clauses. You'll finish by investigating semi joins and anti joins, which provide a nice introduction to subqueries.

    Play Chapter Now
    State of the UNION
    50 xp
    Union
    100 xp
    Union (2)
    100 xp
    Union all
    100 xp
    INTERSECTional data science
    50 xp
    Intersect
    100 xp
    Intersect (2)
    100 xp
    Review union and intersect
    50 xp
    EXCEPTional
    50 xp
    Except
    100 xp
    Except (2)
    100 xp
    Semi-joins and Anti-joins
    50 xp
    Semi-join
    100 xp
    Relating semi-join to a tweaked inner join
    50 xp
    Diagnosing problems using anti-join
    100 xp
    Set theory challenge
    100 xp
  4. 4

    Subqueries

    In this closing chapter, you'll learn how to use nested queries and you'll use what you’ve learned in this course to solve three challenge problems.

    Play Chapter Now
    Subqueries inside WHERE and SELECT clauses
    50 xp
    Subquery inside where
    100 xp
    Subquery inside where (2)
    100 xp
    Subquery inside select
    100 xp
    Subquery inside FROM clause
    50 xp
    Subquery inside from
    100 xp
    Advanced subquery
    100 xp
    Subquery challenge
    100 xp
    Subquery review
    50 xp
    Course review
    50 xp
    Final challenge
    100 xp
    Final challenge (2)
    100 xp
    Final challenge (3)
    100 xp

In the following tracks

Data Analyst Data Analyst SQL FundamentalsSQL Server Fundamentals

Datasets

CountriesLeadersDiagrams

Collaborators

Filip SchouwenaarsColin Ricardo

Prerequisites

Introduction to SQL
Dr. Chester Ismay Headshot

Dr. Chester Ismay

Educator, Data Scientist, and R/Python Consultant

Chester enjoys helping others get into data science, figuring out how to best practice and improve on their skills, and working as a part-time consultant on R and Python programming projects. He is co-author of "Statistical Inference via Data Science: A ModernDive into R and the Tidyverse" available at moderndive.com and for purchase from CRC Press. He likes leading education and data science teams with the goal of improving best practices based on data from the learning sciences.
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