Is there an equivalent to typedef in Transact-SQL?

Is there any way of aliasing datatypes in T-SQL (SQL Server 2005), a bit like a C typedef?开发者_JAVA技巧 I'd like to be able to alias, say, VARCHAR(20) as 'my_datatype' so that wherever I wish to use VARCHAR(20) I could instead use my_datatype.

Synonyms allow you to do this sort of thing for tables, and there are built-in synonyms for some datatypes too, but AFAICS it is not possible to define your own datatype synonyms. Anyone know any different?

What about this

CREATE TYPE  [schema_name.]typename
FROM system_data_type_name [(precision,scale)] [NULL|NOT NULL]

For example

CREATE TYPE CountryCode
FROM char(2) NULL

What you're looking for is User Defined Datatypes, or UDD's.

For SQL Server 2005, you have alias and CLR types. Both use CREATE TYPE

CREATE TYPE perhaps?

For PostgreSQL the syntax is a bit different:

CREATE DOMAIN  [schema_name.]new_typename
AS existing_typename [any_constraint];

For example:

CREATE DOMAIN CountryCode
AS char(2);