Subject Re: [firebird-support] Feature request: Changes in Unique constraint / Unique Index
Author Martijn Tonies

> Yes, I know there are differences, but what they are specifically, I'm not
> sure.
> I mention both since they are in the releaseNote :
> (1.5) NULLs in unique constraints and indices
> Dmitry Yemanov
> .
> ---
> Can a Unique constraints rely on a non unique index, or on no indices at
> all ? As you can see, I don't know what's
> going on in the engine regarding unique constraints / unique indices. But,
> from an Application POV I can't really see any differences. Please set me
> strait if I'm wrong here.

An Unique Constraint automatically creates an index, so there's no
need to add additional indices.

An Unique Index is just that. An unique index.

An Unique Constraint is a candidate key for a table - that means that
it can be used in a Foreign Key Constraint definition -> FKs can
point to columns that make up an Unique Constraint or the Primary
Key Constraint of a table.

So, one can say that an index is something physical (used to quickly
look up table data) while a constraint is something logical.

With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
Upscene Productions