Although a normal Union is generally faster then Join.

What is the difference between union and left join?

The join such as INNER JOIN or LEFT JOIN combines columns from two tables while the UNION combines rows from two queries. In other words, join appends the result sets horizontally while union appends the result set vertically.

Can we use union with join?

To combine data into a single result use both joins and unions. They both go about this is different ways. Difference tables’ columns are combine using a join. The union combines different tables’ rows.