Among the three different types of join operators used by SQL Server, the HASH JOIN does some of the hardest work. It scales pretty well and is very suitable for parallel processing. As such, it can be very powerful in many applications, but hash joins can potentially consume quite a bit of memory, so seeing on in your query plan could be an indicator of a performance tuning issue in your query or data.
There are basically three main types of joins in SQL Server, each one of which has its own characteristics, advantages and drawbacks. You’ll find these three operators in query plans. Knowing how different types joins work will help you optimize your queries, indexing and how to store your data.