Persisting a computed datetime column in SQL Server 2005

Question

I have an XML column in a table; I want to \"promote\" a certain value in that XML as a computed column and index it for faster searching. I have a function that takes in th

Answer 1

What about:

CREATE FUNCTION [dbo].[fComputeValue] (@data XML)
RETURNS varchar(50)
WITH SCHEMABINDING
AS
BEGIN
  RETURN @data.value('(/Metadata/Value[@Key="StartDate"])[1]', 'varchar(50)')
END

and:

ALTER TABLE dbo.CustomMetadataTable ADD [StartDate] AS (convert(datetime,([dbo].[fComputeValue]([CustomMetadataColumn]), 127)) PERSISTED

or:

return convert(datetime, @data.value('(/Metadata/Value[@Key="StartDate"])[1]', 'varchar(50)'), 127)

From books online:

CONVERT is Deterministic unless one of these conditions exists:

Source type is sql_variant.

Target type is sql_variant and its source type is nondeterministic.

Source or target type is datetime or smalldatetime, the other source or target type is a character string, and a nondeterministic style is specified. To be deterministic, the style parameter must be a constant. Additionally, styles less than or equal to 100 are nondeterministic, except for styles 20 and 21. Styles greater than 100 are deterministic, except for styles 106, 107, 109 and 113.

It might help if you use CONVERT with style 127