sql server varchar(max), NVARCHAR(MAX), VARBINARY(MAX) (zz)

Frequently Asked Questions - SQL Server 2005 - VARCHAR(MAX), NVARCHAR(MAX), VARBINARY(MAX)
//z 2012-08-01 14:15:27 is2120@csdn.T995425965 [T7,L192,R3,V122]

 1.  What are the new data types or enhanced data types in SQL Server 2005??

Microsoft SQL Server 2005 introduces a new data type, the XML data type.  The XML data type lets you store XML documents and fragments in a SQL Server database.  An XML fragment is an XML instance that is missing a single top-level element.  You can create columns and variables of XML type and store XML instanced in them.

In addition to the new XML data type, Microsoft SQL Server 2005 has enhanced three of the existing SQL Server data types, namely the VARCHAR(MAX),NVARCHAR(MAX) and VARBINARY(MAX) data types.  The VARCHAR(MAX)data type indicates that the maximum storage size for the VARCHAR data type is 2^31-1 bytes.  The NVARCHAR data types indicates that the maximum storage size fr the NVARCHAR data type is 2^31-1 bytes.  Lastly, the VARBINARY(MAX) data type indicates that the maximum storage size for the VARBINARY data type is 2^31-1 bytes.

 2.  What’s the maximum length for VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX) data types?

The maximum storage size for VARCHAR(MAX) is 2^31-1 bytes (2,147,483,647 bytes or 2GB - 1 bytes).  The storage size is the actual length of data entered + 2 bytes.  The data entered can be 0 characters in length.  Since each character in a VARCHAR data type uses one byte, the maximum length for a VARCHAR(MAX) data type is 2,147,483,645.

The maximum storage size for NVARCHAR(MAX) is also 2^31-1 bytes (2,147,483,647 bytes or 2GB - 1 bytes).  The storage size, in bytes, is two times the number of characters entered + 2 bytes.  The data entered can be 0 characters in length.  Since each Unicode character in an NVARCHAR data type uses two bytes, the maximum length for an NVARCHAR(MAX) data type is 1,073,741,822.

The maximum storage size for VARBINARY(MAX) is the same as the maximum storage size for VARCHAR(MAX) and NVARCHAR(MAX), which is 2^31-1 (2,147,483,647 bytes or 2GB - 1 bytes).  The storage size is the actual length of the data entered + 2 bytes.  The data that is entered can be 0 bytes in length.

 3.  Since you can use VARCHAR(MAX), can I define any length for a VARCHAR data type such as VARCHAR(10000)?

When the the length is specified in declaring a VARCHAR variable or column, the maximum length allowed is still 8000.  If the length is greater than 8000, you have to use the  MAX specifier as the length.  If a length greater than 8000 is specified, the following error will be encountered (assuming that the length specified is 10000):

Server: Msg 131, Level 15, State 3, Line 1
The size (10000) given to the type 'varchar' exceeds the maximum allowed for any data type (8000).

 4.  Will VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX) replace TEXT, NTEXT and IMAGE data types?
//z 2012-08-01 14:15:27 is2120@csdn.T995425965 [T7,L192,R3,V122]

Yes, VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX) will replace the TEXT, NTEXT and IMAGE data types, respectively.  TEXT, NTEXT and IMAGE data types will be removed in the future version of Microsoft SQL Server.  Avoid using these data types when using SQL Server 2005 and use VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX)instead.

 5. Can I declare a local variable of VARCHAR(MAX), NVARCHAR(MAX) or VARBINARY(MAX)?

Yes, you can declare local variables of VARCHAR(MAX), NVARCHAR(MAX)and VARBINARY(MAX) data types.  This is unlike the data types that these enhanced data types are replacing because declaring local variables of TEXT, NTEXT and IMAGE data types is not allowed.  You will encounter the following error message when a local variable of TEXT, NTEXT or IMAGE data type is defined:

Server: Msg 2739, Level 16, State 1, Line 7
The text, ntext, and image data types are invalid for local variables.

 6.  If there are VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX) data types, are there also CHAR(MAX), NCHAR(MAX) and BINARY(MAX) data types?

No, there is no CHAR(MAX), NCHAR(MAX) or BINARY(MAX).  The main reason why the MAX specifier is not included for these data types is because these data types are fixed-length data.  If the MAX specifier was included for these data types, it will be a big waste of disk space as each column will consume 2GB-1 bytes even if only a short string value is assigned to the column.

 7.  How can I make sure that my VARCHAR column will only contain 10,000 characters?  Defining it as VARCHAR(10000) generates an error of "The size (10000) given to the type 'varchar' exceeds the maximum allowed for any data type (8000)."

To create a column of VARCHAR data type with a maximum of 10,000 characters, you declare the column as VARCHAR(MAX) data type and simply add a CHECK constraint to the column by checking the length of the column and making sure it is less than or equal to 10,000 characters.  To illustrate, here's how it will look like:

CREATE TABLE [dbo].[VarChar10000] ( [VarChar10000] VARCHAR(MAX) )
GO

ALTER TABLE [dbo].[VarChar10000] 
    ADD CONSTRAINT [MaxLength10000]
    CHECK (DATALENGTH([VarChar10000]) <= 10000)
GO

With the column defined as VARCHAR(MAX), it can accept a string longer than 8,000 characters.  But with the CHECK constraint, it will not allow a string with a length of more than 10,000 characters.  To verify that the column will not allow a string of more than 10,000 characters, try executing the following INSERT command, which will insert a string value of 11,000 characters:

INSERT INTO [dbo].[VarChar10000] ( [VarChar10000] )
VALUES (REPLICATE(CAST('A' AS VARCHAR(MAX)), 11000))

The following error will be shown when the INSERT statement above is executed:

Server: Msg 547, Level 16, State 1, Line 1
The INSERT statement conflicted with the CHECK constraint "MaxLength10000".
The conflict occurred in database, table "dbo.VarChar10000", column 'VarChar10000'.
The statement has been terminated.

//z 2012-08-01 14:15:27 is2120@csdn.T995425965 [T7,L192,R3,V122]