The define business key dialog will appear asking for the business key that will uniquely identify each normalized table record. The source table from which the normalized table is derived would normally have some form of unique constraint applied. In most cases this will be the business key. In the example below the customer code is selected as the business key.

A business key can be made up of multiple columns, but it must provide a unique identifier. Where multiple columns separately uniquely identify rows in the normalized table, choose one to act as the primary business key. For example a source table may have a unique constraint on both a product code and a product description. Therefore the description as well as the code must be unique. It is of course possible to combine the two columns, but the normal practice would be to choose the code as the business key.

None of the columns chosen as the business key should ever contain a NULL value. See the note at the start of this chapter.