From time to time I got a question about the difference between unique key and unique constraint. Both elements enforcing uniqueness across values in column(s). But the unique index cannot be used in referential integrity constraints. The unique index can be considered as a “tool” for unique constraint.
Jiří Činčura is .NET, C# and Firebird expert. He focuses on data and business layers, language constructs, parallelism, databases and performance. For almost two decades he contributes to open-source, i.e. FirebirdClient. He works as a senior software engineer for Microsoft. Frequent speaker and blogger at www.tabsoverspaces.com.