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From Aman Sinha <asi...@maprtech.com>
Subject Join affinity
Date Fri, 24 Jul 2015 18:47:37 GMT
In many situations we want to  have some kind of join 'affinity' for a pair
of tables T1, T2  where these 2 tables must be joined to each other before
being joined to any other table.

Two such situations are:
1.   SELECT * FROM t1, t2 WHERE t1.a1 IN (1, 2, 3.....thousands) AND t1.b1
= t2.b2
      Here, the IN list can be represented by a VALUES operator and exposed
as a table
      to be joined to t1.  It is important to do this join first before
joining t1 to t2.
           - This might be addressed by doing a SemiJoin instead of inner
join.  Would that
              be the right approach ?

2.  SELECT * FROM t1,  t1_dimension, t2 WHERE  ....
     Here, I want to join t1 and t1_dimension before joining t1 with t2.
The reason is
     t1_dimension has a column that is the primary key of t1, so if there
is a filter on a
     dimension column, I can get the corresponding primary keys and do the
join with t1.
     One can think of t1_dimension as basically an index table for t1.
        -  For this case, I don't want to rely on costing since the join
planning may not
           necessarily pick the join order I want.   Is there a good way to
achieve this in
           Calcite ?

thanks,
Aman

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