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R5'. All other NestedTupleSourceOperators in the subplan is inlined with the query plan rooted at O1.

This is an abstract example for the special rewriting mechanism described above: 

Before rewriting:

--Op1

  --Subplan{

    --AggregateOp

      --NestedOp

        – Join (J1)

          – ..... (L1)

             --Nested-Tuple-Source

          – ..... (R1)

    }

    --InputOp

      .....

After rewriting:

-- Op1

  – GroupBy v_lc_1, ..., v_lc_n Decor v_l1, ....v_ln {

            – AggregateOp

               – NestedOp

                 – Select v_new!=NULL

                   – Nested-Tuple-Source

          }

     --LeftOuterJoin (J1)

       (left branch)

           – Assign v_new=TRUE

              –  ......  (L1)

                 – InputOp

                   .....

       (right branch)

            – ..... (R1)

In the plan, v_lc_1, ..., v_lc_n are live "covering" variables at InputOp, while v_rc_1, ..., v_rc_n are their corresponding variables populated from the deepcopy of InputOp. "Covering" variables form a set of variables that can imply all live variables. v_l1, ....v_ln in the decoration part of the added group-by operator are all live variables at InputOp except the covering variables v_lc_1, ..., v_lc_n.  In the current implementation, we use "covering" variables as primary key variables. In the next version, we will use the real primary key variables, which will fix ASTERIXDB-1168.

Here is a concrete example (optimizerts/queries/nested_loj2.aql). .

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