Is there an equivalent to typedef in Transact-SQL?

Question

Is there any way of aliasing datatypes in T-SQL (SQL Server 2005), a bit like a C typedef? 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?

Answer 1

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

Answer 2

您正在寻找的是用户定义的数据类型或UDD。

Answer 3

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

Answer 4

或许创造类型？

Answer 5

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);