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  2. Cardinality (SQL statements) - Wikipedia

    en.wikipedia.org/wiki/Cardinality_(SQL_statements)

    This column would contain unique values of 1-n. Each time a new user is created in the USERS table, a new number would be created in the USER_ID column to identify them uniquely. Since the values held in the USER_ID column are unique, this column's cardinality type would be referred to as high-cardinality.

  3. Unique key - Wikipedia

    en.wikipedia.org/wiki/Unique_key

    In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.

  4. Surrogate key - Wikipedia

    en.wikipedia.org/wiki/Surrogate_key

    Having the key independent of all other columns insulates the database relationships from changes in data values or database design [5] (making the database more agile) and guarantees uniqueness. In a temporal database, it is necessary to distinguish between the surrogate key and the business key. Every row would have both a business key and a ...

  5. Identity column - Wikipedia

    en.wikipedia.org/wiki/Identity_column

    An identity column differs from a primary key in that its values are managed by the server and usually cannot be modified. In many cases an identity column is used as a primary key; however, this is not always the case. It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to ...

  6. Relational database - Wikipedia

    en.wikipedia.org/wiki/Relational_database

    Each row in a table has its own unique key. Rows in a table can be linked to rows in other tables by adding a column for the unique key of the linked row (such columns are known as foreign keys). Codd showed that data relationships of arbitrary complexity can be represented by a simple set of concepts. [2]

  7. Check constraint - Wikipedia

    en.wikipedia.org/wiki/Check_constraint

    Check constraints are used to ensure the validity of data in a database and to provide data integrity. If they are used at the database level, applications that use the database will not be able to add invalid data or modify valid data so the data becomes invalid, even if the application itself accepts invalid data.

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  9. Second normal form - Wikipedia

    en.wikipedia.org/wiki/Second_normal_form

    To make the design conform to 2NF, it is necessary to have two relations. To create these relations: Remove the functionally dependent attributes in the partial dependencies of the first normal form relation. In this example, {Manufacturer country} is the functionally dependent attribute which will be removed.