# Supporting uniqueness constraints

A column that has a uniqueness constraint must have a unique value for every record.

Primary key columns automatically require uniqueness. Uniqueness can also be required for other columns. For example, in a `users` table, `userid` is the primary key column, but `username` also must be unique.

The following generators can be used with columns that have uniqueness constraints:

* [Alphanumeric String Key](/app/generation/generators/generator-reference/alphanumeric-string-key.md)
* [ASCII Key](/app/generation/generators/generator-reference/ascii-key.md)
* [Character Substitution](/app/generation/generators/generator-reference/character-substitution.md)
* [Conditional](/app/generation/generators/generator-reference/conditional.md)
* [Finnish Personal Identity Code](/app/generation/generators/generator-reference/finnish-personal-identity-code.md)
* [FNR](/app/generation/generators/generator-reference/fnr.md)
* [Geo](/app/generation/generators/generator-reference/geo.md)
* [IBAN](/app/generation/generators/generator-reference/iban.md)
* [Integer Key](/app/generation/generators/generator-reference/integer-key.md)
* [Null](/app/generation/generators/generator-reference/null.md)
* [Numeric String Key](/app/generation/generators/generator-reference/numeric-string-key.md)
* [Passthrough](/app/generation/generators/generator-reference/passthrough.md)
* [Random UUID](/app/generation/generators/generator-reference/random-uuid.md)
* [Regex Mask](/app/generation/generators/generator-reference/regex-mask.md)
* [Sequential Integer](/app/generation/generators/generator-reference/sequential-integer.md)
* [SIN](/app/generation/generators/generator-reference/sin.md)
* [Unique Email](/app/generation/generators/generator-reference/unique-email.md)
* [URL](/app/generation/generators/generator-reference/url.md)
* [UUID Key](/app/generation/generators/generator-reference/uuid-key.md)


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