SQL joins are fundamental operations in relational databases. They allow us to combine data from two or more tables based on a related column. Imagine you have a table of customers and a table of orders. A join allows you to see which customer placed which order. Different types of joins exist, each with its own purpose and behavior. A Venn diagram can help visualize how different join types combine data. The overlapping areas represent the common data, while the non-overlapping areas represent data unique to each table. Understanding the different join types is vital for constructing accurate and efficient queries. For example, an inner join only returns rows where a match exists in both tables, while a left join returns all rows from the left table, even if there's no match in the right table. This flexibility is essential for extracting the right information from your database.