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Add SET ANSI_NULLS ON before CREATE TABLE statement

To create a unique index is required that the table be created with the
'ANSI_NULLS ON' setting.

MSSQL uses the configuration of server when this configuration is ommited. Until
SQL Server 2012, the default is 'ANSI_NULLS OFF', but new versions will be
defined with 'ON'.

To avoid problems with different servers (and their configurations) is a good
pratice execute 'SET ANSI_NULLS' before table creation.