Unique non-key fields

[toma42]

Create an index on the field and specify that the index must be unique. Consult your specific database documentation for the syntax.

[Anon]

How would I specify in the table definition that a field must be unique even when it is not a primary key?

[[deleted]]

Various databases let you define columns as unique without creating an index.
Read the manual of your database.

[kparker]

without creating an index

Do you perhaps mean, "without making it a primary key"? If someone has a system out there that enforces uniqueness without using a btree or a hash or something similar, I'd like to hear about it.

For example, PostgreSQL certainly uses indexes to implement uniqueness: the difference between primary-key definitions and unique definitions is that in the latter, you are also allowed to have null values.

[[deleted]]

No, I mean "without making an index", meaning that you don't have to "alter table add index" or similar to create a unique column.

How the database handles it technically is interesting but it gets confusing. 🙂