-- syntax for creating a function-based index:
 
    CREATE [UNIQUE] INDEX index_name
      ON table_name (function1, function2, . function_n)
      [ COMPUTE STATISTICS ];
 
 
-- for example:
 
    CREATE INDEX supplier_metrics
       ON supplier (UPPER(supplier_city));
 
-- to be sure that the Oracle optimizer uses this index 
-- when executing your SQL statements, be sure that 
-- UPPER(supplier_city) does not evaluate to a NULL value. 
-- To ensure this, add UPPER(supplier_city) IS NOT NULL to 
-- your WHERE clause as follows:
 
    SELECT supplier_id, supplier_city, UPPER(supplier_city)
    FROM supplier
    WHERE UPPER(supplier_city) IS NOT NULL
    ORDER BY UPPER(supplier_city);