Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/906#discussion_r136182353
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/ProjectPrel.java
---
@@ -35,18 +35,43 @@
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.sql.SqlKind;
+/**
+ * A physical Prel node for Project operator.
+ */
public class ProjectPrel extends DrillProjectRelBase implements Prel{
static final org.slf4j.Logger logger =
org.slf4j.LoggerFactory.getLogger(ProjectPrel.class);
+ private final boolean outputProj;
public ProjectPrel(RelOptCluster cluster, RelTraitSet traits, RelNode
child, List<RexNode> exps,
RelDataType rowType) {
+ this(cluster, traits, child, exps, rowType, false);
+ }
+
+ /**
+ * Constructor for ProjectPrel.
+ * @param cluster
+ * @param traits traits of ProjectPrel node
+ * @param child input
+ * @param exps list of RexNode, representing expressions of projection.
+ * @param rowType output rowType of projection expression.
+ * @param outputProj true if ProjectPrel is inserted by {@link
org.apache.drill.exec.planner.physical.visitor.TopProjectVisitor}
+ * Such top Project operator does the following
processing, before the result was presented to Screen/Writer
+ * 1) ensure final output field names are preserved,
+ * 2) handle cases where input does not return any
batch (a fast NONE) (see ProjectRecordBatch.handleFastNone() method)
+ * 3) handle cases where expressions in upstream
operator were evaluated to NULL type
--- End diff --
Done.
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