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?

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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

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

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

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CREATE TYPE perhaps?

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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);