Hash Indexing may improve performance on large data types, like VARCHAR in PostgreSQL. But, TSQL does not support Hash Indexing. In this case, we can still manually create a hash value and index it.
http://msdn.microsoft.com/en-us/library/ms191241(v=sql.105).aspx
http://stackoverflow.com/questions/318219/sql-server-hash-indexes
http://clay.lenharts.net/blog/2008/02/03/sql-server-hash-indexes/
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