When set to the default of "On" (true, yes), A_MSSQL_ADD_IDENTITY adds an extra column to any table created by Database Connectors for MSSQL. The extra column will have the identity property and will be included on all indexes that are not unique. Otherwise, when A_MSSQL_ADD_IDENTITY is set to "False" (false, no), no extra column is added.
Example
A_MSSQL_ADD_IDENTITY TRUE
On keys that allow duplicates, this variable has been found to vastly improve performance. Note that the default value is "True" for a file that allows duplicates and is "False" for a file with no duplicate keys.