An integral part of many SQL queries are SQL subqueries. They make it possible to retrieve data from the database more efficiently and precisely by allowing for complicated queries, dynamic filtering, and calculations based on the outcomes of other queries. However, proper application is key, as with any method. The best SQL techniques, types, and scope of SQL subqueries are covered in this material:
https://www.devart.com/dbforge/sql/studio/sql-subqueries-with-examples.html