Data type synonyms (Transact-SQL)

APPLIES TO: yesSQL Server (starting with 2012) noAzure SQL Database noAzure SQL Data Warehouse noParallel Data Warehouse

Data type synonyms are included in SQL Server for ISO compatibility. The following table lists the synonyms and the SQL Server system data types that they map to.

Synonym SQL Server system data type
Binary varying varbinary
char varying varchar
character char
character char(1)
character( n ) char(n)
character varying( n ) varchar(n)
Dec decimal
Double precision float
float[(n)] for n = 1-7 real
float[(n)] for n = 8-15 float
integer int
national character( n ) nchar(n)
national char( n ) nchar(n)
national character varying( n ) nvarchar(n)
national char varying( n ) nvarchar(n)
national text ntext
timestamp rowversion

Data type synonyms can be used instead of the corresponding base data type name in data definition language (DDL) statements, such as CREATE TABLE, CREATE PROCEDURE, or DECLARE @variable. However, after the object is created, the synonyms have no visibility. When the object is created, the object is assigned the base data type that is associated with the synonym. There is no record that the synonym was specified in the statement that created the object.

All objects that are derived from the original object, such as result set columns or expressions, are assigned the base data type. All subsequent metadata functions performed on the original object and any derived objects will report the base data type, not the synonym. This behavior occurs with metadata operations, such as sp_help and other system stored procedures, the information schema views, or the various data access API metadata operations that report the data types of table or result set columns.

For example, you can create a table by specifying national character varying:

CREATE TABLE ExampleTable (PriKey int PRIMARY KEY, VarCharCol national character varying(10))  

VarCharCol is actually assigned an nvarchar(10) data type, and all subsequent metadata functions will report the column as an nvarchar(10) column. The metadata functions will never report them as a national character varying(10) column.

See also

Data Types (Transact-SQL)