Two SQL queries.

SELECT DISTINT service_ID from .....

Fetch into array and loop...
foreach (serviceID)
{
  SELECT stop_reference, distance from XXX
  WHERE service_ID = :p1
    AND distance = (SELECT min(distance) from XXX where service_id = :
+p1)
  
}
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I'm sure some SQL guru can wrap this all into one SQL query. In Oracle, you could use PL/SQL to get this, too. But even in pure SQL you should be able to do this without a loop. I'm just not an SQL guru. :(