Create User-Defined Table Type

使用 Create type 创建自定义的Table Type ，Syntax 如下，和Create Table的 语法十分相似。

CREATE TYPE [ schema_name. ] type_name
{
    FROM base_type
    [ ( precision [ , scale ] ) ]
    [ NULL | NOT NULL ]
  | AS TABLE ( { <column_definition> | <computed_column_definition> }
        [ <table_constraint> ] [ ,...n ] )
} [ ; ]

<column_definition> ::=
column_name <data_type>
    [ COLLATE collation_name ]
    [ NULL | NOT NULL ]
    [
        DEFAULT constant_expression ]
      | [ IDENTITY [ ( seed ,increment ) ]
    ]
    [ ROWGUIDCOL ] [ <column_constraint> [ ...n ] ] 

<column_constraint> ::=
{     { PRIMARY KEY | UNIQUE }
        [ CLUSTERED | NONCLUSTERED ]
        [ WITH ( <index_option> [ ,...n ] ) ]
  | CHECK ( logical_expression )
} 

<table_constraint> ::=
{
    { PRIMARY KEY | UNIQUE }
        [ CLUSTERED | NONCLUSTERED ]
         ( column_name [ ASC | DESC ] [ ,...n ] )
        [ WITH ( <index_option> [ ,...n ] )]
    | CHECK ( logical_expression )
} 

Examples

1，Creating an alias type based on the varchar data type

CREATE TYPE dbo.PhoneNum
FROM varchar(11) NOT NULL ;

2,Creating a user-defined table type

/* Create a user-defined table type */
CREATE TYPE dbo.LocationTableType
AS TABLE
(
LocationID bigint not null primary key clustered,
LocationName VARCHAR(50) not null,
CostRate float check(CostRate between 0.0 and 1.0)
)
GO

3,drop user-defined type

drop type dbo.LocationTableType

Remarks  

The DROP TYPE statement will not execute when any of the following is true:

• There are tables in the database that contain columns of the alias data type or the user-defined type. Information about alias or user-defined type columns can be obtained by querying the sys.columns or sys.column_type_usages catalog views.
• There are computed columns, CHECK constraints, schema-bound views, and schema-bound functions whose definitions reference the alias or user-defined type. Information about these references can be obtained by querying the sys.sql_expression_dependencies catalog view.
• There are functions, stored procedures, or triggers created in the database, and these routines use variables and parameters of the alias or user-defined type. Information about alias or user-defined type parameters can be obtained by querying the sys.parameters or sys.parameter_type_usages catalog views.

参考doc：

CREATE TYPE (Transact-SQL)

DROP TYPE (Transact-SQL)