DROP TYPE (Transact-SQL)
Removes an alias data type or a common language runtime (CLR) user-defined type from the current database.
The DROP TYPE statement will not execute when any of the following is true:
There are tables in the database that contain columns of the alias data type or the user-defined type. Information about alias or user-defined type columns can be obtained by querying the sys.columns or sys.column_type_usages catalog views.
There are computed columns, CHECK constraints, schema-bound views, and schema-bound functions whose definitions reference the alias or user-defined type. Information about these references can be obtained by querying the sys.sql_expression_dependencies catalog view.
There are functions, stored procedures, or triggers created in the database, and these routines use variables and parameters of the alias or user-defined type. Information about alias or user-defined type parameters can be obtained by querying the sys.parameters or sys.parameter_type_usages catalog views.
For more information about investigating alias and user-defined type references, see Implementing User-defined Types.
The following example assumes a type named ssn is already created in the current database.
DROP TYPE ssn ;