The SQL DISTINCT clause isn’t case sensitive, which means that your query might end up pulling records with different cases.

A simple fix for this is to use the COLLATE clause in conjunction with the DISTINCT clause.

Use sql_latin1_general_cp1_ci_ai for case sensitive distinct clause:

a) CASE INSENSITIVE DISTINCT CLAUSESELECT DISTINCT (Item) COLLATE sql_latin1_general_cp1_cs_as    FROM (           SELECT  'a' item 	   UNION ALL SELECT  'A'	 )itemsb) CASE SENSITIVE DISTINCT CLAUSESELECT DISTINCT (Item) COLLATE sql_latin1_general_cp1_ci_ai    FROM (           SELECT  'a' item	   UNION ALL SELECT  'A'	 ) items