Question

I want to perform a select which returns a few columns of data, and then also a nested table of related rows from another table (actually the same table joined on itself but I think this is irrelevant).

So the data is something like this:

id  name   registered
1   Dan      N
2   Bill     N
3   Bob      N
4   Dan      N
5   Bill     Y
6   Dan      Y

The idea is to perform a select which finds all the unregistered people who could be related to a registered account.

So the result would look like

registered.id   name   notreg.id   name
  5             Bill     2          Bill
  6             Dan      1          Dan
                         4          Dan

I can handle all the selection criteria etc, and have a query that returns a normal inner join that finds this, but want to know if it’s possible to get a result set kind of like this, so no repeated values on the left side?

Answer 1

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

However on anything that supports a WITH (CTE) 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_NUMBER 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