Introduction to SQL JOIN
Understanding the relationships between different tables within a database is crucial for manipulating and extracting meaningful data. A key aspect of this understanding comes from the use of SQL JOINs. In SQL, a “JOIN” is an integral operation that allows for the combination of data from two or more tables based on a related column, or columns, between them. This relational operation forms the cornerstone of most database queries, which involve dealing with more than a single table.
There are several types of JOINs available in SQL, each serving its unique purpose depending on the specific requirement of the query. These are:
- INNER JOIN
- LEFT (OUTER) JOIN
- RIGHT (OUTER) JOIN
- FULL (OUTER) JOIN
- CROSS JOIN
- SELF JOIN
Here is a cheatsheet for SQL JOINs for you to refer back to if necessary. Don’t worry if you don’t understand this right now as we will go over each of these JOIN types in great detail.
As we proceed, we will delve into the intricacies of each of these JOIN types, exploring their distinct functionalities with examples. Let’s take a look at them together!
Before we do that, if you would like a quick refresher, take a look at this SQL Cheatsheet to get familiar with the basics.