![]() ![]() You get the error message because it found a duplicate key for the column. You can see it creates a unique non-clustered index for the table.Ĭlick Ok and save the modifications you did. We also have the few options enabled for unique Indexes such as Ignore duplicate keys and Re-compute statistics.Ĭlose this index/keys page and generate the script. Right-click on, select Index/keys, and choose Index from the Type column. It opens the table designer as we saw earlier. Let’s right-click on table and select Design. Previously we created unique constraints in SQL Server using the SSMS GUI method. It provides you with an additional benefit that no one can accidentally delete the unique Index created by the We can verify in the following screenshot that Index does not exist now. I modified the table name to have an appropriate name for our demo. Table and unique constraint in SQL Server. We use the generated script to create the ![]() It is a good thing, especially forĬlick on the Generate Change Script…, and you get t-SQL for Create table, add primary keyĬonstraint and add the unique constraint in SQL Server.Ĭopy this script and close the table designer window without saving it. SSMS gives you the option to generate the script for the work you did on the GUI. We cannot make anyĬhange here because the unique key is for unique value in a column. Let’s select the Unique Key, and you see that the previous option “Is Unique” is greyed out. In the type, you get an option to choose from the Unique key or Index. In this SQL Server index properties, we can select a value for the property- IsUnique. Select the data sort order in ascending (default) or descending order. In the General group, select the column in which we want to define a SQL Server Index. It opens the following indexes/keys wizard that shows existing indexes like we already have a primary key onĬlick on Add, and we can define additional index/constraints using this. Now, right-click on the column and choose Indexes/Keys. It puts a key symbol for the primary key column, as shown below. Right-click on the column and enable the Primary Key by clicking Set Primary key on it. Specify columns, their data type and remove the check for the Allow Nulls column. Expand the database and right-click on Tables-> ![]() Let’s create a SQL table using the SSMS GUI method. We do not have the option to define the primary key because We do not want anyĭuplicate value in this social security number column. ![]() This table also holds the social security number of employees. Suppose you have an employee table and as its name suggests it holds all employee’s information. You might beįamiliar with a primary key column that also enforces unique value in the column. It prevents you from having duplicate values in columns tied with the unique constraint. It can be either on a single column or a combination ofĬolumns. We can ensure unique value in a column of SQL Server. Overview of UNIQUE constraints in SQL Server In this article, we will explore SQL Server Unique Indexes and Unique constraints. Transaction Overview to learn about ACID properties. You can go through this article, SQL Server It means that only valid data that satisfies the condition should exist in the database. We use Constraints for the Consistency property of an ACID. Isolation and Durability for a SQL Server transaction. SQL Server enforces ACID properties – Atomicity, Consistency, We can add a constraint using the Create table or Alter table statement. We will look at the differences between them.Ĭonstraints in SQL Server allows defining the rules at the column level in the SQL table. This article gives you an overview of Unique Constraints in SQL and also the Unique SQL Server index. ![]()
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