How to Alter User Defined Table Type in SQL Server
User defined table types (UDTTs) in SQL Server are a powerful feature that allows users to create custom table types. These custom types can be used to define the structure of tables that can be passed as parameters to stored procedures, functions, or table-valued parameters. However, there may be instances where you need to alter a user defined table type after it has been created. This article will guide you through the process of altering a user defined table type in SQL Server.
Understanding User Defined Table Types
Before diving into the alteration process, it’s important to have a clear understanding of what user defined table types are. A UDTT is essentially a custom data type that is defined by the user. It can contain columns, constraints, and other properties similar to a regular table. Once created, UDTTs can be used as a data type for columns, parameters, and return types in stored procedures, functions, and triggers.
Steps to Alter a User Defined Table Type
To alter a user defined table type in SQL Server, follow these steps:
1. Identify the UDTT you want to alter. You can find the name of the UDTT by querying the `sys.types` system view.
2. Use the `ALTER TYPE` statement to modify the UDTT. The syntax for altering a UDTT is as follows:
“`sql
ALTER TYPE [schema_name].[type_name]
ALTER COLUMN [column_name] [data_type] [column_constraints]
“`
Replace `[schema_name]` with the schema name, `[type_name]` with the name of the UDTT, `[column_name]` with the name of the column you want to alter, `[data_type]` with the new data type, and `[column_constraints]` with any additional constraints you want to apply.
3. Execute the `ALTER TYPE` statement to apply the changes to the UDTT.
Here’s an example of altering a UDTT:
“`sql
— Altering a UDTT named ‘EmployeeUDTT’
ALTER TYPE [dbo].[EmployeeUDTT]
ALTER COLUMN [EmployeeID] INT NOT NULL;
“`
In this example, we are altering the `EmployeeUDTT` by changing the `EmployeeID` column to an `INT` data type and setting it as `NOT NULL`.
Considerations and Best Practices
When altering a user defined table type, it’s important to consider the following:
– Ensure that the changes you make to the UDTT do not break any dependencies. For example, if a stored procedure uses the UDTT, make sure that the changes do not cause any errors in the stored procedure.
– Be cautious when altering columns that are already in use. For instance, changing the data type of a column that contains existing data may lead to data loss or corruption.
– Always back up your database before making any significant changes to the UDTTs or other database objects.
By following these steps and considerations, you can successfully alter user defined table types in SQL Server to meet your evolving requirements.
