How do you suppress or hide duplicate values in SQL?

Question

I\'ve been looking around for a bit and have not been able to find out how to do this yet (though have found alot about analyzing it\'s performance?!)

I want to perform

Answer 1

You're probably better off suppressing duplicates it in the Client (for example in Jasper Reports uncheck Print Repeated Value or in the XML set isPrintRepeatedValues="false")

However on anything that supports WITH and ROW_NUMBER() (e.g. Oracle, SQL Server 2005+) .

WITH ns 
         AS (SELECT Row_number() OVER (PARTITION BY name ORDER BY id) rn, 
                    id, 
                    name, 
                    registered 
             FROM   t 
             WHERE  registered = 'N') 
    SELECT t.id, 
           t.name, 
           ns.id, 
           ns.name 
    FROM   ns 
           LEFT JOIN t 
             ON ns.name = t.name 
                AND t.registered = 'Y' 
                AND ns.rn = 1 
    WHERE  ns.name IN (SELECT name 
                       FROM   t 
                       WHERE  registered = 'Y')  

    ORDER  BY ns.name 

See working example

If you don't have WITH and ROW_NUIMBER you can do this

SELECT t.id, 
       t.name, 
       ns.id, 
       ns.name 
FROM   t ns 
       LEFT JOIN (SELECT MIN(id) id, 
                         name 
                  FROM   t 
                  WHERE  registered = 'N' 
                  GROUP  BY name) MINNS 
         ON ns.id = MINNS.id 
       LEFT JOIN t 
         ON ns.name = t.name 
            AND t.registered = 'Y' 
            AND MINNS.id IS NOT NULL 
WHERE  ns.registered = 'N' 
       AND ns.name IN (SELECT name 
                       FROM   t 
                       WHERE  registered = 'Y') 
ORDER  BY ns.name, 
          ns.id

See working example