In Power BI, joins are primarily used in Power Query (during the "Merge Queries" step) to combine data from two separate tables based on a common column or relationship. Power BI supports six main types of joins, each serving a specific data combination need: 1. Left Outer Join This is the most common join. It keeps all rows from the first (left) table and adds matching data from the second (right) table. If a row on the left does not have a match on the right, Power BI will return null (blank)