Extension tables is one of the two types of master data tables that you can create yourself. There are two types of extensions: product extensions and customer extensions. The name extension comes from the fact that these tables are used to add information to product and customer master data. Product extensions have a foreign key field sku that relates each row to a product; while the customer extension have a field customerId that relates each row to a customer.

Extension tables share tables in the relational database, and are differentiated by the name column. The name column specifies which extension table the row belongs to. For example:

The frontend application displays the rows of different extensions on different pages — creating the impression that they are in fact different tables. In the example above, sku-00043 and sku-00233 are displayed on the ProductCost page; while the other two rows appear on the ProductPackaging page.

Since the extensions are stored on the same table in the relational database, you need to consider this when you build your queries. In the example above, if you only want to include rows from the ProductCost table among the results, you need to include a filter for the name column in your query.