How to Alter User Defined Datatype in SQL Server 2012
In SQL Server 2012, user-defined datatypes (UDTs) provide a way to create custom data types that can be used to store complex data structures. These UDTs can be used to define a structure that is not available in the standard data types provided by SQL Server. However, there may be situations where you need to alter an existing UDT to accommodate changes in your data model or business requirements. This article will guide you through the process of altering a user-defined datatype in SQL Server 2012.
Understanding User-Defined Datatypes
Before diving into the process of altering a UDT, it’s important to have a clear understanding of what UDTs are and how they work. A UDT is a data type that you define using the CREATE TYPE statement. It can contain one or more columns, each with its own data type. UDTs can be used to create tables, views, and stored procedures, and they can also be used as the data type for a column in a table.
Steps to Alter a User-Defined Datatype
To alter a user-defined datatype in SQL Server 2012, follow these steps:
1. Identify the UDT that you want to alter. You can do this by querying the INFORMATION_SCHEMA.TABLE_TYPES view or by using the sys.types catalog view.
2. Use the ALTER TYPE statement to modify the UDT. The syntax for the ALTER TYPE statement is as follows:
“`sql
ALTER TYPE [schema_name].[type_name]
ADD column_name column_type [NULL|NOT NULL] [CONSTRAINT constraint_name]
“`
For example, if you want to add a new column named “Age” of type INT to a UDT named “EmployeeType”, you would use the following statement:
“`sql
ALTER TYPE [dbo].[EmployeeType]
ADD Age INT NULL
“`
3. If you need to remove a column from the UDT, you can use the DROP COLUMN clause in the ALTER TYPE statement. For example, to remove the “Age” column from the “EmployeeType” UDT, you would use the following statement:
“`sql
ALTER TYPE [dbo].[EmployeeType]
DROP COLUMN Age
“`
4. If you need to change the data type of a column in the UDT, you can use the ALTER COLUMN clause in the ALTER TYPE statement. For example, to change the data type of the “Age” column from INT to SMALLINT, you would use the following statement:
“`sql
ALTER TYPE [dbo].[EmployeeType]
ALTER COLUMN Age SMALLINT
“`
5. After making the necessary changes to the UDT, you may need to update any tables, views, or stored procedures that use the UDT to reflect the changes. This can be done by modifying the schema of the affected objects.
Conclusion
Altering a user-defined datatype in SQL Server 2012 can be a straightforward process if you follow the correct steps. By understanding the structure of UDTs and using the ALTER TYPE statement, you can easily modify your custom data types to meet your evolving data model and business requirements. Always ensure that you have a backup of your database before making any changes to UDTs, as altering them can have a significant impact on your database schema.
