Primary Key

In the relational model of database design, a unique key or primary key is a set of attributes whose values uniquely define the characteristics of each row. The primary key has to consist of characteristics that cannot collectively be duplicated by any other row. In an entity relationship diagram of a data model, one or more unique keys may be declared for each data entity. Each unique key is composed from one or more data attributes of that data entity. The set of unique keys declared for a data entity is often referred to as the candidate keys for that data entity. From the set of candidate keys, a single unique key is selected and declared the primary key for that data entity.
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    … has logged into the app, a token_for_business field will be present on the User object and added to the signed request passed to Canvas apps. This emits a token that is stable for the same person across multiple apps owned by the same business. This new token has a few specific characteristics: It’s a token, not an ID. As such, it cannot be used…

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