Compare SQL Server 2008 value to linked excel file

Are you comparing an entire Excel sheet to a table, or just a single value in a single cell in an Excel sheet to some value in some table in SQL Server? Comparing the sheet to a table can be done, but it's a bit longer - a single value shouldn't be much trouble at all.

You'd use OPENROWSET to open a connection to your Excel sheet, and then you can query it just like a table and get the value you're interested in. First, make sure that "Ad Hoc Distributed Queries" is enabled, since you'll be querying an external datasource on the fly, and it's an advanced option:

EXEC sp_configure 'Ad Hoc Distributed Queries', 1 
RECONFIGURE

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Once that's done, you can connect to your Excel sheet:

SELECT * FROM OPENDATASOURCE('Microsoft.Jet.OLEDB.4.0',
   'Data Source=c:\YourFolder\YourExcelSheet.xls;Extended Properties=Excel 8.0')...[Sheet1$]

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That will give you the contents of your sheet as a resultset. You can either modify that query to fetch only the value you want, or (and it may be easier depending on what you're doing) you can insert all those contents into a temp table and work with them there, comparing them to your internal SQL Server value.

If you still need some more helping getting this accomplished and you post some more details about what you're trying to do, I can help you refine the query.