Couchbase different result of nested loop WHERE clause - couchbase

Question

I am facing a wierd issue in couchbase: i was executing the following two queries:
SELECT *
FROM (
SELECT *
FROM (
SELECT *
FROM ssb_lineorder
LIMIT 10000) AS cte0
INNER JOIN ssb_ddate ON cte0.ssb_lineorder.lo_orderdate = ssb_ddate.d_datekey) AS cte1
JOIN ssb_part USE NL ON cte1.cte0.ssb_lineorder.lo_partkey = ssb_part.p_partkey
WHERE ssb_part.p_size > 10
and
SELECT *
FROM (
SELECT *
FROM (
SELECT *
FROM (
SELECT *
FROM ssb_lineorder
LIMIT 10000) AS cte0
INNER JOIN ssb_ddate ON cte0.ssb_lineorder.lo_orderdate = ssb_ddate.d_datekey) AS cte1
JOIN ssb_part USE NL ON cte1.cte0.ssb_lineorder.lo_partkey = ssb_part.p_partkey ) AS cte2
WHERE cte2.ssb_part.p_size > 10
These two are exactly the same except the final WHERE clause. According to my knowledge of relational DBMS, the results should be exactly the same. but I am getting different result: 1 for the first query, 7972 for the second query.
I am wondering if I misunderstood the n1ql mechenism ?

Answer 1

There should not be any different.
LIMIT inside without order by can cause inconsistent results. 1 vs 7972 that is way off.
As this data dependent you need to debug that.
Execute UI and go to Plan Text tab and take look ItemsIn#, ItemsOut# of each operator and take look where things gone wrong.
Also add predicate and reduce data and see what is wrong.
As no OUTER JOIN try the following.
CREATE INDEX ix1 ON ssb_part(p_size, p_partkey);
CREATE INDEX ix2 ON ssb_lineorder(lo_partkey, lo_orderdate);
CREATE INDEX ix3 ON ssb_ddate(d_datekey);
SELECT *
FROM ssb_part AS sp
JOIN ssb_lineorder AS sl ON sp.p_partkey = sl.lo_partkey
JOIN ssb_ddate AS sd ON sl.lo_orderdate = sd.d_datekey
WHERE sp.p_size > 10
SELECT *
FROM ssb_part AS sp
JOIN ssb_lineorder AS sl USE HASH (PROBE) ON sp.p_partkey = sl.lo_partkey
JOIN ssb_ddate AS sd USE HASH (PROBE) ON sl.lo_orderdate = sd.d_datekey
WHERE sp.p_size > 10 ;