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MS SQL Server - Microsoft SQL Server - User Defined Table Types
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  creating a UDT with a single int column that is also a primary key 
CREATE TYPE dbo.Ids as TABLE
(
    Id int PRIMARY KEY
)
  Creating a UDT with multiple columns 
CREATE TYPE MyComplexType as TABLE
(
    Id int,
    Name varchar(10)
)
  Creating a UDT with a unique constraint: 
CREATE TYPE MyUniqueNamesType as TABLE
(
    FirstName varchar(10),
    LastName varchar(10),
    UNIQUE (FirstName,LastName)
)

Note: constraints in user defined table types can not be named.
  Creating a UDT with a primary key and a column with a default value: 
CREATE TYPE MyUniqueNamesType as TABLE
(
    FirstName varchar(10),
    LastName varchar(10),
    CreateDate datetime default GETDATE()
    PRIMARY KEY (FirstName,LastName)
)

Remarks

UDTs have following restrictions -

  • can not be used as a column in a table or a field in a structured user-defined types
  • a non-clustered index cannot be created in a UDT unless the index is the result of creating a PRIMARY KEY or UNIQUE constraint on the UDT
  • UDT definition CANNOT be modified after it is created
 

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