Bad result from grouping query with nested order by and limit

What steps will reproduce the problem?

let $sample :=
{{
  {"r": 1, "uid": "1a2b", "t": datetime("2000-01-01T01:00:00"), "event": "e1"},
  {"r": 2, "uid": "1a2b", "t": datetime("2000-01-01T01:01:00"), "event": "e2"},
  {"r": 3, "uid": "3c4d", "t": datetime("2000-01-01T01:02:00"), "event": "e1"},
  {"r": 4, "uid": "3c4d", "t": datetime("2000-01-01T01:03:00"), "event": "e3"},
  {"r": 5, "uid": "1a2b", "t": datetime("2000-01-01T01:04:00"), "event": "e1"},
  {"r": 6, "uid": "1a2b", "t": datetime("2000-01-01T01:05:00"), "event": "e4"}
}}
for $s1 in $sample
for $s2 in $sample
where $s1.uid = $s2.uid
  and $s1.t < $s2.t
let $pair := { "s1": $s1, "s2": $s2 }
group by $s1.uid, $s1.t with $pair
let $next := 
    for $p in $pair
    order by $p.s2.t
    limit 1
    return $p
return $next

This should return all adjacent pairs of events for each uid; it returns the 
right number of results but the last three are empty for some reason:

[ { "s1": { "r": 1, "uid": "1a2b", "t": datetime("2000-01-01T01:00:00.000Z"), 
"event": "e1" }, "s2": { "r": 2, "uid": "1a2b", "t": 
datetime("2000-01-01T01:01:00.000Z"), "event": "e2" } } ]
[  ]
[  ]
[  ]

Original issue reported on code.google.com by dtab...@gmail.com on 12 Jul 2013 at 9:28

br1ghtyang / asterixdb

Bad result from grouping query with nested order by and limit #567