SQL Server Storage sql_variant

USE tempdb ;
GO

DROP TABLE tbl ;
GO

CREATE TABLE tbl
(
i SQL_VARIANT NOT NULL
) ;
GO

INSERT INTO tbl (i)
VALUES (1) ;
GO

SELECT i FROM tbl ;
GO

DBCC IND ('tempdb','tbl',-1) ;
GO

DBCC TRACEON (3604) ; -- Page dump will go the console
GO

DBCC PAGE ('tempdb',1,157,3) ;
GO

• Record Size = 17B

• 30000400 01000001 00110038 01010000 00

• TagA = 0x30 = 1B

• TagB = 0x00 = 1B

• Null Bitmap Offset = 0x0004 = 2B

• Column Count = 0x0001 = 2B

• Null Bitmap = 0x00 = 1B

• Variable-Length Columns Count = 0x0001 = 2B

• Variable-Length Column Offset Array = 0x0011 = 2B

• This is the sql_variant encoding for integers...I guess = 0x0138 = 2B

• Our integer column = 0x00000001 = 4B

SELECT
SQL_VARIANT_PROPERTY(i , 'BaseType') AS BaseType -- SYSNAME NVARCHAR(128)
, SQL_VARIANT_PROPERTY(i , 'Precision') AS [Precision] -- INT
, SQL_VARIANT_PROPERTY(i , 'Scale') AS Scale -- INT
, SQL_VARIANT_PROPERTY(i , 'TotalBytes') AS TotalBytes -- INT
, SQL_VARIANT_PROPERTY(i , 'Collation') AS [Collation] -- SYSNAME NVARCHAR(128)
, SQL_VARIANT_PROPERTY(i , 'MaxLength') AS MaxLength -- INT
FROM
tbl ;
GO

My questions:

• 0x3801...what is that

• i = 328792402 Huh? Where did this come from?

• SQL_VARIANT_PROPERTY() says I have an integer. Why does it not choose tinyint?

• Does anyone know where SQL_VARIANT_PROPERTY() can be found. Must I use the DAC to get at it?

The first 2 answers are from the SQL Server Internals Book p.278

• 0x38 is 56 in decimal. This indicates int in sys.types (system_type_id column)

• 0x01 is the version number of the sql_variant format (always 1 in SQL Server 2008)

• This is the way the literal 1 is always interpreted in SQL Server. e.g. SELECT 1 AS foo INTO NewTable will create a new column of integer datatype. Use an explicit cast if you want it to be treated as a different datatype.

• This is part of the product source code. You cannot view the definition.

BTW: If you are looking at other datatypes as well you may encounter some additional bytes between the version number and the column value as follows.

• numeric/decimal have 1 byte each for precision and scale.

• [n][var]char have 2 bytes for max length and 4 bytes for collation id.

• [var]binary have 2 bytes for max length.

StackExchange Database Administrators Q#14778, answer score: 8