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In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...
In relational database management systems, a unique key is a candidate key.All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the primary key of the relation.
Hi/Lo is an algorithm and a key generation strategy used for generating unique keys for use in a database as a primary key. It uses a sequence-based hi-lo pattern to generate values. Hi/Lo is used in scenarios where an application needs its entities to have an identity prior to persistence. It is a value generation strategy.
Tables are linked by "key fields". A "primary key" assigns a field to its "special order table". For example, the "Doctor Last Name" field might be assigned as a primary key of the Doctor table with all people having same last name organized alphabetically according to the first three letters of their first name.
Entity integrity is concerned with ensuring that each row of a table has a unique and non-null primary key value; this is the same as saying that each row in a table represents a single instance of the entity type modelled by the table.
Oracle NoSQL Database is a client-server, sharded, shared-nothing system. The data in each shard are replicated on each of the nodes that comprise the shard. The major key for a record is hashed to identify the shard that the record belongs to.
Oracle has its own spin where creating a user is synonymous with creating a schema. Thus a database administrator can create a user called PROJECT and then create a table PROJECT.TABLE. Users can exist without schema objects, but an object is always associated with an owner (though that owner may not have privileges to connect to the database).
While an overall database key article is useful (and Key (database) is a better name than unique key), "primary key" is a common term, and deserves its own article. Many of the comments at Talk:Unique key ask for clarification on what a primary key is, and how it differs from a unique key.