Q:

Distinct value in two column

I have a query in mysql
select f1,f2,f3 from tableName;

I want to remove duplicate value in field f1 and f2 only,
I have tired as follows
select f1,f2,f3 from tableName
group by f1,f2;

But it will remove duplicates in f1 only. Any body can suggest me that how to remove duplicates in f1 and f2. 
topic_id    topic_name                    question_type
2237    Understanding Diversity           Comprehensive
2237    Understanding Diversity           Easy
2237    Understanding Diversity           Application
44315   Bhasha, boli, lipi, or Vayakaran  Intermediate

above is sample output having distinct value in question_type column only
here i want to remove duplicates from question_type and topic_id
expected output: having both topic_id and question_type distinct values
 44315  Bhasha, boli, lipi, or Vayakaran  Intermediate
 2237   Understanding Diversity           Comprehensive

A:

My SQL really isn't that great, but I think you need to do what is called a nested SELECT statement. 
Here is the manual reference. 
http://dev.mysql.com/doc/refman/5.0/en/subqueries.html
That would make the SQL look something like this. 
SELECT f1,f2,f3 FROM (SELECT f1,f2,f3 FROM tableName AS table1 GROUP BY f1) AS table2 GROUP BY f2;

Note, that I had to use the AS to create an alias, else "tableName" would conflict with the parent SQL select.