A maximum of 20 distinct fields can be used to define a primary key. The number of fields used in the primary key limits the number of fields in the secondary keys. Fields used by one key can also be used in another key; however, no more than 20 unique fields can be used to create primary or secondary keys.
This means that if your primary key includes four distinct fields, your secondary keys can include these four fields, and at most 16 other fields. Correspondingly, if your primary key consists of 20 distinct fields, then your secondary keys must consist only of combinations of these fields.
When you create a table in Table Designer, by default Microsoft Dynamics NAV uses the field with the lowest field number as the primary key. Use the following procedure to define a different primary key.
To define a primary key
On the Tools menu, choose Object Designer.
Choose Table.
Select a table from the list and then choose Design.
Select the first empty line and then from the View menu, choose Keys.
The Keys window appears.
In the first line of the Keys window, enter the primary key as a comma-delimited list; for example, "ID Number, Name".
Defining Secondary Keys
Up to 40 keys can be defined for a table. The first key defined is the primary key. All the other keys are secondary keys and are optional. Secondary keys are used to view records in an order that is different from the order defined by the primary key fields.
To define a secondary key
On the Tools menu, choose Object Designer.
Choose Table.
Select a table from the list and then choose Design.
Select the first empty line and then from the View menu, choose Keys.
The Keys window appears.
The first line shows the primary key. Enter the secondary keys on the following lines as comma-separated lists; for example: Name, Address.