Problem: Connect Join to Project in the SQL API

[Kristian Reitzel]

Hi Dev,

We are working on the Join Operator in the SQL API.

After connecting the two table scans of type Record, the output slots of the 
join operator is of type Tuple2.

This confuses us since we would expect the result of a join to be of type 
Record. Furthermore, the projection (which happens after the join) throws the 
following Exception:

Exception in thread "main" java.lang.IllegalArgumentException: Cannot connect 
out@Join[2->1, id=23ad2d17] of DataSetType[BasicDataUnitType[Tuple2]] to 
in@Map[1->1, id=6bce4140] of type DataSetType[BasicDataUnitType[Record]].
                at 
org.apache.wayang.core.plan.wayangplan.Operator.connectTo(Operator.java:206)
                at 
org.apache.wayang.api.sql.calcite.converter.WayangProjectVisitor.visit(WayangProjectVisitor.java:42)
                at 
org.apache.wayang.api.sql.calcite.converter.WayangRelConverter.convert(WayangRelConverter.java:16)
                at 
org.apache.wayang.api.sql.calcite.optimizer.Optimizer.convert(Optimizer.java:202)
                at 
org.apache.wayang.api.sql.context.SqlContext.executeSql(SqlContext.java:92)
                at SqlAPI.examplePostgres(SqlAPI.java:46)
                at SqlAPI.main(SqlAPI.java:77)

We tried changing the Wayang MapOperator inputTypeClass to be a Tuple2, but 
this does not fix the problem.

Is there anyone that can explain why the JoinOperator outputs a Tuple2 and 
perhaps also how we then connect the output of the join to the input of the 
projection?

Best,
Michelle and Kristian