SQL Server user-defined data types

User-defined data type: Based on the system data type, it is generated by the database administrator.
Use system stored procedures to define user-defined data types` Sp_addtype [@typename=] new data type name, 　　[@phystype=] system data type name 　　[,[@nulltype=] null_type] 　　[,[@owner=] owner_name] 　　system Data type names, except "BIG, INT, SMALLINT, TEXT, DATETIME, REAL, UNIQUE IDENTIFIER, IMAGE", must be enclosed in single quotes.　　　　null_type: The way the new data type handles null values, it can be NOT NULL or NULL, the default is null 　　owner_name: The owner of the new data type, the default is the current user.
　　

E.g:

/* Create custom data type */ 
Exec sp_addtype a, ' char(10) ' 
Exec sp_addtype da, datetime , ' null ' 
/* Delete custom data type */ 
Exec sp_droptype a