data-konzept

'The ability to combine results from related rows from multiple tables is an important part of relational database system design. In SQL Server, this is accomplished with the SQL join clause.  It’s the nature of traditional relational database systems where some table contains information related to other tables with a common key value. Using a SQL join, you can easily perform queries on related data-sets from multiple tables with these shared keys.

The aim of this article is to provide you with the basic knowledge and examples that you will need to use the SQL join effectively in any database environment.'...

https://www.sqlshack.com/sql-join-overview-and-tutorial/