How to Alter User Defined Datatype in SQL Server 2008

In SQL Server 2008, user-defined datatypes (UDTs) allow users to create custom data types that can be used to store data in a more structured and meaningful way. These datatypes can be used to enhance the integrity and usability of your database. However, there may be instances where you need to alter an existing user-defined datatype. This article will guide you through the process of altering a user-defined datatype in SQL Server 2008.

Understanding User-Defined Datatypes

Before diving into the alteration process, it is essential to have a clear understanding of user-defined datatypes. A UDT is a data type created by the user to represent a structured set of data. It can be used as a column data type, a table data type, or a parameter data type. UDTs can be defined using the CREATE TYPE statement and can include various data types such as strings, integers, decimals, and even other UDTs.

Steps to Alter a User-Defined Datatype

To alter a user-defined datatype in SQL Server 2008, follow these steps:

1. Identify the UDT that needs to be altered. You can find the UDT by querying the INFORMATION_SCHEMA.TABLE_TYPES or the sys.types catalog view.

2. Once you have identified the UDT, use the ALTER TYPE statement to modify the UDT. The syntax for altering a UDT is as follows:

“`sql
ALTER TYPE [schema_name].[user_defined_type_name]
MODIFY (property_name = property_value);
“`

Replace [schema_name] with the name of the schema containing the UDT, and [user_defined_type_name] with the name of the UDT.

3. Specify the property you want to alter and provide the new value for that property. For example, if you want to change the maximum length of a string UDT, you can use the following syntax:

“`sql
ALTER TYPE [schema_name].[user_defined_type_name]
MODIFY (max_length = 100);
“`

4. Execute the ALTER TYPE statement to apply the changes to the UDT.

Example

Suppose you have a UDT named “EmployeeDetails” with two properties: “FirstName” (string) and “Age” (integer). You want to change the maximum length of the “FirstName” property from 50 to 100. The following ALTER TYPE statement will achieve this:

“`sql
ALTER TYPE [YourSchemaName].[EmployeeDetails]
MODIFY (FirstName max_length = 100);
“`

Conclusion

Altering user-defined datatypes in SQL Server 2008 is a straightforward process that can be performed using the ALTER TYPE statement. By following the steps outlined in this article, you can modify existing UDTs to better suit your database requirements. Remember to always test your changes in a non-production environment before applying them to your live database.