How to Enforce Unique Constraints on Column Combinations in SQL Server?

Make sure the unique sex constraints of the SQL Server column combination

The database table may have multiple records that have the same columns. To avoid this situation, you can force the implementation of unique constraints and require the combination of a specific column to be unique in the table.

For example, one table contains the following column:

ID (main key)

• name
Active
Personnumber
• It is required to ensure that there is only one record with Personnumber and Active = 1.

Create unique sexual constraints

After deleting any repeated records in the table, you can use statement or sentence to add unique constraints.

Method ALTER TABLE CREATE UNIQUE INDEX

Method

ALTER TABLE

Repeat

<code class="language-sql">ALTER TABLE dbo.yourtablename
  ADD CONSTRAINT uq_yourtablename UNIQUE(column1, column2);</code>

CREATE UNIQUE INDEX You can actively check the potential conflict, rather than let the SQL Server process repeated insertions by returning anomalies.

<code class="language-sql">CREATE UNIQUE INDEX uq_yourtablename
  ON dbo.yourtablename(column1, column2);</code>

Check the conflict

In order to prevent abnormal interrupt applications, you can use the following methods:

The performance effects of different error treatment technology:

Consider the performance effects of various error treatment methods.

Check the potential constraints before entering Try/Catch:

Check the potential conflict before entering the abnormal processing block to reduce the overhead.

Use Instead of trigger
• If you want to process repeated insertions without modifying the application, you can create an Instead of trigger:
• Example
The following examples demonstrate the creation of unique sexual constraints and verifying its functions on the column combination:

This example demonstrates the duplicate records of the unique constraint on how to prevent having the same Personnumber and Active = 1 combination.

The above is the detailed content of How to Enforce Unique Constraints on Column Combinations in SQL Server?. For more information, please follow other related articles on the PHP Chinese website!