SQL Joins — A Simple Guide

If you are working with SQL relational databases, at some point you are going to use JOINs. Normalized data is organized and spread across multiple tables, oftentimes linked by a common column key (or multiple keys). We use JOINs to bring the data together. Therefore JOINs are an important concept to grasp. There are SQL JOIN articles and guides across the internet far and wide and I am adding one more into the mix…

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I am using Oracle SQL for the example JOIN queries in this post. The SQL implementation you are using should have comparable JOINs. However, all SQL databases are not exactly the same so be sure and consult the documentation for your vendor for any specific questions or clarification.

The example queries for this post are derived from the 2 tables shown below. They are both super simple in structure and design, each containing a single NUMBER column named NUM_COL with INTEGER values: