Prior to SQL Server 2017, relationships in graph structures were represented by junction tables. SQL Server 2017 supports graph databases by bringing graph extensions called SQL Graph features. SQL Graph and graph extensions are part of the SQL Server database engine. You don't need to install separate services; as soon as you install SQL Server, you can use SQL graph capabilities in all SQL Server editions.

In SQL Server 2017, you can create two types of graph objects, node and edge tables, and use the new MATCH clause to traverse through the graph. Node and edge tables are normal tables with some special columns and attributes. A graph is a collection of node and edge tables, and all tables within a database belong to the same graph. Since node and edge tables are SQL Server tables, you are allowed to create regular relationships between the tables.

To support the creation and alteration of graph tables, the CREATE/ALTER TABLE Transact-SQL statements have been extended in SQL Server 2017.