When expression is a date or time data type, style can be one of the values shown in the following table. Other values are processed as 0. SQL Server supports the date format in Arabic style by using the Kuwaiti algorithm.

1 These style values return nondeterministic results. Includes all (yy) (without century) styles and a subset of (yyyy) (with century) styles.

2 The default values (style 0 or 100, 9 or 109, 13 or 113, 20 or 120, and 21 or 121) always return the century (yyyy).

3 Input when you convert to datetime; output when you convert to character data.

4 Designed for XML use. For conversion from datetime or smalldatetime to character data, the output format is as described in the previous table.

5 Hijri is a calendar system with several variations. SQL Server uses the Kuwaiti algorithm.

6 Only supported when casting from character data to datetime or smalldatetime. When character data that represents only date or only time components is cast to the datetime or smalldatetime data types, the unspecified time component is set to 00:00:00.000, and the unspecified date component is set to 1900-01-01.

7The optional time zone indicator, Z, is used to make it easier to map XML datetime values that have time zone information to SQL Server datetime values that have no time zone. Z is the indicator for time zone UTC-0. Other time zones are indicated with HH:MM offset in the + or - direction. For example: 2006-12-12T23:45:12-08:00.

When you convert to character data from smalldatetime, the styles that include seconds or milliseconds show zeros in these positions. You can truncate unwanted date parts when you convert from datetime or smalldatetime values by using an appropriate char or varchar data type length.

When you convert to datetimeoffset from character data with a style that includes a time, a time zone offset is appended to the result.

When expression is float or real, style can be one of the values shown in the following table. Other values are processed as 0.

When expression is money or smallmoney, style can be one of the values shown in the following table. Other values are processed as 0.

When expression is xml, style can be one of the values shown in the following table. Other values are processed as 0.

When expression is binary(n), varbinary(n), char(n), or varchar(n), style can be one of the values shown in the following table. Style values that are not listed in the table return an error.

Implicit conversions are those conversions that occur without specifying either the CAST or CONVERT function. Explicit conversions are those conversions that require the CAST or CONVERT function to be specified. The following illustration shows all explicit and implicit data type conversions that are allowed for SQL Server system-supplied data types. These include xml, bigint, and sql_variant. There is no implicit conversion on assignment from the sql_variant data type, but there is implicit conversion to sql_variant.

Large-value data types exhibit the same implicit and explicit conversion behavior as their smaller counterparts, specifically the varchar, nvarchar and varbinary data types. However, you should consider the following guidelines:

• Conversion from image to varbinary(max) and vice-versa is an implicit conversion, and so are conversions between text and varchar(max), and ntext and nvarchar(max).
   
• Conversion from large-value data types, such as varchar(max), to a smaller counterpart data type, such as varchar, is an implicit conversion, but truncation will occur if the large value is too big for the specified length of the smaller data type.
   
• Conversion from varchar, nvarchar, or varbinary to their corresponding large-value data types is performed implicitly.
   
• Conversion from the sql_variant data type to the large-value data types is an explicit conversion.
   
• Large-value data types cannot be converted to the sql_variant data type. 

When you explicitly or implicitly cast the xml data type to a string or binary data type, the content of the xml data type is serialized based on a set of rules. For information about these rules, see Serialization of XML Data. For information on how to cast from XML to a CLR user-defined type, see Performing Operations on User-defined Types. For information about how to convert from other data types to the xml data type, see Generating XML Instances.

Automatic data type conversion is not supported for the text and image data types. You can explicitly convert text data to character data, and image data to binary or varbinary, but the maximum length is 8000 bytes. If you try an incorrect conversion such as trying to convert a character expression that includes letters to an int, SQL Server returns an error message.

When the output of CAST or CONVERT is a character string, and the input is a character string, the output has the same collation and collation label as the input. If the input is not a character string, the output has the default collation of the database, and a collation label of coercible-default. For more information, see Collation Precedence (Transact-SQL).

To assign a different collation to the output, apply the COLLATE clause to the result expression of the CAST or CONVERT function. For example:

SELECT CAST('abc' AS varchar(5)) COLLATE French_CS_AS

When you convert character or binary expressions (char, nchar, nvarchar, varchar, binary, or varbinary) to an expression of a different data type, data can be truncated, only partially displayed, or an error is returned because the result is too short to display. Conversions to char, varchar, nchar, nvarchar, binary, and varbinary are truncated, except for the conversions shown in the following table.

* = Result length too short to display. E = Error returned because result length is too short to display.

SQL Server guarantees that only roundtrip conversions, conversions that convert a data type from its original data type and back again, will yield the same values from version to version. The following example shows such a roundtrip conversion:

The following example shows a resulting expression that is too small to display.

Here is the result set.

When you convert data types that differ in decimal places, sometimes the result value is truncated and at other times it is rounded. The following table shows the behavior.

For example, the result of the following conversion is 10:

SELECT CAST(10.6496 AS int)

When you convert data types in which the target data type has fewer decimal places than the source data type, the value is rounded. For example, the result of the following conversion is $10.3497:

SELECT CAST(10.3496847 AS money)

SQL Server returns an error message when nonnumeric char, nchar, varchar, or nvarchar data is converted to int, float, numeric, or decimal. SQL Server also returns an error when an empty string (" ") is converted to numeric or decimal.

FirstName      LastName         Title                  Sick Leave
---------      ---------      -------------------   -----------
Gustavo        Achong         Mr.                   *
Catherine      Abel           Ms.                   *
Kim            Abercrombie    Ms.                   *
Humberto       Acevedo        Sr.                   *
Pilar          Ackerman       Sra.                  *

(5 row(s) affected)

USE AdventureWorks;
GO
SELECT c.FirstName, c.LastName, SUBSTRING(c.Title, 1, 25) AS Title, 
       CAST(e.SickLeaveHours AS char(1)) AS 'Sick Leave'
FROM HumanResources.Employee e 
     JOIN Person.Contact c ON e.EmployeeID = c. ContactID
WHERE NOT EmployeeID >5

DECLARE @myval decimal (5, 2)
SET @myval = 193.57
SELECT CAST(CAST(@myval AS varbinary(20)) AS decimal(10,5))
-- Or, using CONVERT
SELECT CONVERT(decimal(10,5), CONVERT(varbinary(20), @myval))

In SQL Server 2000, string to date and time conversions are marked as deterministic. However, this is not true for the styles listed in the following table. For these styles, the conversions depend on the language settings. SQL Server 2005 and later versions mark these conversions as nondeterministic.

The following table lists the styles for which the string-to-datetime conversion is nondeterministic.

1 With the exception of styles 20 and 21