Oracle SQL hiding duplicate values

Question

I have a query with these results:

A | 1
A | 2
B | 1
B | 2
B | 3

How do I get the results to be like this:

A | 1
  | 2  
B | 1   
  | 2   
  | 3

Answer 1

Here is one way:

SELECT CASE WHEN rn = 1 THEN c1 ELSE NULL END || ' | ' || c2
  FROM (SELECT c1, c2, ROW_NUMBER() OVER (PARTITION BY c1 ORDER BY c2) rn
          FROM your_table);