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  2. Foreign key - Wikipedia

    en.wikipedia.org/wiki/Foreign_key

    A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...

  3. Data definition language - Wikipedia

    en.wikipedia.org/wiki/Data_definition_language

    Another type of DDL sentence in SQL is used to define referential integrity relationships, usually implemented as primary key and foreign key tags in some columns of the tables. These two statements can be included in a CREATE TABLE or an ALTER TABLE sentence;

  4. Unique key - Wikipedia

    en.wikipedia.org/wiki/Unique_key

    Here ID serves as the primary key in the table 'Author', but also as AuthorID serves as a Foreign Key in the table 'Book'. The Foreign Key serves as the link, and therefore the connection, between the two related tables in this sample database. In a relational database, a candidate key uniquely identifies each row of data values in a database ...

  5. Relational database - Wikipedia

    en.wikipedia.org/wiki/Relational_database

    The primary keys within a database are used to define the relationships among the tables. When a PK migrates to another table, it becomes a foreign key (FK) in the other table. When each cell can contain only one value and the PK migrates into a regular entity table, this design pattern can represent either a one-to-one or one-to-many relationship.

  6. Surrogate key - Wikipedia

    en.wikipedia.org/wiki/Surrogate_key

    When inspecting a row holding a foreign key reference to another table using a surrogate key, the meaning of the surrogate key's row cannot be discerned from the key itself. Every foreign key must be joined to see the related data item. If appropriate database constraints have not been set, or data imported from a legacy system where ...

  7. Walmart's Cyber Monday deals are extended — here are 10 you ...

    www.aol.com/lifestyle/walmarts-cyber-monday...

    We've spent the last week covering just about Cyber Monday deal we thought our AOL readers would love: orthopedic sneakers at 50% off, $20 Sam's Club memberships, and even sweaters you can get ...

  8. Associative entity - Wikipedia

    en.wikipedia.org/wiki/Associative_entity

    An associative (or junction) table maps two or more tables together by referencing the primary keys (PK) of each data table. In effect, it contains a number of foreign keys (FK), each in a many-to-one relationship from the junction table to the individual data tables. The PK of the associative table is typically composed of the FK columns ...

  9. When are the fourth College Football Playoff rankings ...

    www.aol.com/fourth-college-football-playoff...

    The College Football Playoff will soon release its fourth top 25 rankings of the season. Here’s what you need to know and how to watch.