Data Keys are used to establish and identify relations between tables. They ensure that each record within a table can be uniquely identified by combination of one or more fields within a table. Relational Tables support the following Keys:
Primary Key (PK)
Column that contains a unique identifier. Data in this column/field cannot be duplicated. The Primary Key cannot contain NULL, and only one may exist per table. The Primary Key can only be in STRING or NUMBER data type. A Primary Key must be defined before a Table can be activated.
Foreign Key (FK)
Column that establishes the relationship between two Tables. The Foreign Key must be defined during Table creation as it is required for a Table to be activated. Relational Tables support Foreign Keys for regular tables with no limit on the depth unless otherwise defined in the Account Settings, where the default is set to three.
Multi-Foreign Key (FK)
Allows a table to be related to multiple tables. A table can be related to multiple tables. Relational Tables support up to four Multi-Foreign Keys for a Join Table; no more than three Flat tables and one Regular Table or the system Subscriber table.