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  2. Composite key - Wikipedia

    en.wikipedia.org/wiki/Composite_key

    In database design, a composite key is a candidate key that consists of two or more attributes, [1] [2] [3] (table columns) that together uniquely identify an entity occurrence (table row). A compound key is a composite key for which each attribute that makes up the key is a foreign key in its own right.

  3. Entity integrity - Wikipedia

    en.wikipedia.org/wiki/Entity_integrity

    Each of attributes being part of a PK (or of a FK) must have data values (such as numbers, letters or typographic symbols) but not data marks (also known as NULL marks in SQL world). Morphologically, a composite primary key is in a "steady state": If it is reduced, PK will lose its property of identifying every row of its relation but if it is ...

  4. Unique key - Wikipedia

    en.wikipedia.org/wiki/Unique_key

    A key that may become the primary key. Primary The key that is selected as the primary key. Only one key within an entity is selected to be the primary key. This is the key that is allowed to migrate to other entities to define the relationships that exist among the entities.

  5. 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 ...

  6. Relational database - Wikipedia

    en.wikipedia.org/wiki/Relational_database

    The surrogate key has no intrinsic (inherent) meaning, but rather is useful through its ability to uniquely identify a tuple. Another common occurrence, especially in regard to N:M cardinality is the composite key. A composite key is a key made up of two or more attributes within a table that (together) uniquely identify a record. [20]

  7. Database normalization - Wikipedia

    en.wikipedia.org/wiki/Database_normalization

    Recall that the Book table below has a composite key of {Title, Format}, which will not satisfy 2NF if some subset of that key is a determinant. At this point in our design the key is not finalised as the primary key, so it is called a candidate key. Consider the following table:

  8. Your money, the economy, taxes might change in 2025 ... - AOL

    www.aol.com/money-economy-taxes-might-change...

    A new president, a strong economy and tons of innovation: How those and other forces might change economic, tax and financial situations in 2025.

  9. Relational model - Wikipedia

    en.wikipedia.org/wiki/Relational_model

    A table in a SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries correspond to predicates. However, SQL databases deviate from the relational model in many details, and Codd fiercely argued against deviations that compromise the original principles. [3]