约束SQLServer中唯一性约束的作用与意义（sqlserver唯一性）

Unique Constraints and their Meaning in SQL Server

When designing a database, it’s important to understand the different types of constraints and their meaning in SQL Server. One type of constraint is the unique constraint. The unique constraint goes by many names, such as the unique key, primary key, and alternate key. All these terms mean the same thing: the unique constraint enforces the no-duplication rule in a database. By designating a field or set of fields as unique, the unique constraint ensures that all records have unique values for the designated fields. This rule is enforced on all records in the table(s), and for any created or modified records.

What are the benefits of using a unique constraint? There are several. First, it ensures data integrity. By keeping records unique, you avoid instances of duplicate records or data entry errors. It also provides an indexable, searchable field to find the associated information in the database. Does the table need to be searched on the designated field? By having an index or unique constraint associated with it, a search can be accomplished quickly and accurately.

How do you implement a unique constraint in SQL Server? It’s fairly easy. You start by creating a unique index on the designated field or fields. This can be done through the Object Explorer within SQL Server: right-click the table in question, select “Indexes / Keys”, and then select “New Unique Index…” In the ensuing dialog, fill in the name of the index, the fields to be indexed, and any additional options you wish (such as index creation permissions). After that, the unique index is created and enforced.

In summary, unique constraints are a fundamental part of relational database design and implementation. They ensure data integrity and provide searchable fields that make data lookup easy and accurate. Implementing them in SQL Server is straightforward, and should be a fundamental part of any database design.