Many-to-many relationships between tables are accommodated in databases by means of junction tables. A junction table contains primary key columns of two tables you want to relate.
To create a many-to-many relationship between tables in dbForge Fusion for SQL Server you need to:
Create/Open a database diagram.
Add the tables that you want to create a many-to-many relationship between.
Create a third table by right-clicking within the database diagram, and then clicking New Table.
This will become a junction table.
In the table editor dialog box, enter a name for the table.
For example, the junction table between the Customer table and the Supplier table is named CustomerSupplier.
Copy the primary key columns from each of the other two tables to the junction table.
You can add other columns to this table, just as you can to any other table.
In the junction table, set a primary key to include all primary key columns from the other two tables.
Define a one-to-many relationship between each of the two primary tables and the junction table.
The creation of a junction table in a database diagram does not insert data from the related tables into the junction table. You can copy rows from one table to another or within a table using an Insert From query.