AI engineering glossary · SQL databases
What is UNIQUE (unique constraint)?
Unique constraint (also called UNIQUE): A rule that no two rows may hold the same value (or combination of values) in the chosen column(s). Unlike a primary key, the column may allow NULL in many systems, and a table can have several such rules.
Unique constraint: an example
UNIQUE(email) ensures two accounts cannot register with the same email address.
Related terms
More SQL databases terms
Where you learn it
Unique constraint is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.