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  2. Primary key - Wikipedia

    en.wikipedia.org/wiki/Primary_key

    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 ...

  3. Database index - Wikipedia

    en.wikipedia.org/wiki/Database_index

    Database systems usually implicitly create an index on a set of columns declared PRIMARY KEY, and some are capable of using an already-existing index to police this constraint. Many database systems require that both referencing and referenced sets of columns in a FOREIGN KEY constraint are indexed, thus improving performance of inserts ...

  4. Entity integrity - Wikipedia

    en.wikipedia.org/wiki/Entity_integrity

    A requirement of E. F. Codd in his seminal paper is that a primary key of an entity, or any part of it, can never take a null value. [1] The relational model states that every relation (or table ) must have an identifier, called the primary key (abbreviated PK), in such a way that every row of the same relation be identifiable by its content ...

  5. Relational database - Wikipedia

    en.wikipedia.org/wiki/Relational_database

    The use of efficient indexes on both primary and foreign keys can dramatically improve query performance. This is because B-tree indexes result in query times proportional to log(n) where n is the number of rows in a table and hash indexes result in constant time queries (no size dependency as long as the relevant part of the index fits into ...

  6. Candidate key - Wikipedia

    en.wikipedia.org/wiki/Candidate_key

    The columns in a candidate key are called prime attributes, [3] and a column that does not occur in any candidate key is called a non-prime attribute. Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that isn't minimal, some subset of that ...

  7. Structured type - Wikipedia

    en.wikipedia.org/wiki/Structured_type

    Student_Type then could be used in order to create a Student_Table which will include all columns defined in Person_Type as well.Primary Key and Constraints should be defined during or after creation of table and cannot be defined inside structure type itself.

  8. Referential integrity - Wikipedia

    en.wikipedia.org/wiki/Referential_integrity

    For referential integrity to hold in a relational database, any column in a base table that is declared a foreign key can only contain either null values or values from a parent table's primary key or a candidate key. [2] In other words, when a foreign key value is used it must reference a valid, existing primary key in the parent table.

  9. TimesTen - Wikipedia

    en.wikipedia.org/wiki/TimesTen

    To utilize Oracle Database caching, one defines one or more SQL objects known as cache groups. A cache group is a set of one or more related database tables and allows for subsets of its rows and/or columns. Database tables in a cache group must each have a defined primary key or a unique index declared across a set of non-nullable columns and ...