Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/906#discussion_r134630528
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/project/ProjectRecordBatch.java
---
@@ -768,4 +765,73 @@ else if (exprHasPrefix && refHasPrefix) {
}
}
}
+
+ /**
+ * handle FAST NONE specially when Project for query output. This
happens when input returns a
+ * FAST NONE directly ( input does not return any batch with
schema/data).
+ *
+ * Project operator has to return a batch with schema derived using the
following 3 rules:
+ * Case 1: * ==> expand into an empty list of columns.
+ * Case 2: regular column reference ==> treat as nullable-int column
+ * Case 3: expressions => Call ExpressionTreeMaterialization over an
empty vector contain.
+ * Once the expression is materialized without error, use the
output type of materialized
+ * expression.
+ * The batch is constructed with the above rules, and recordCount = 0.
+ * Returned with OK_NEW_SCHEMA to down-stream operator.
+ */
+ @Override
+ protected IterOutcome handleFastNone() {
+ if (! popConfig.isOutputProj()) {
+ return super.handleFastNone();
+ }
+
+ allocationVectors = new ArrayList<>();
+ final List<NamedExpression> exprs = getExpressionList();
+ final ErrorCollector collector = new ErrorCollectorImpl();
+ VectorContainer fakedIncomingVC = new VectorContainer();
+
+ for (NamedExpression namedExpression : exprs) {
+ if (namedExpression.getExpr() instanceof SchemaPath) {
+ final NameSegment expr = ((SchemaPath)
namedExpression.getExpr()).getRootSegment();
+ if (expr.getPath().contains(StarColumnHelper.STAR_COLUMN)) {
--- End diff --
`expr.getPath().contains(StarColumnHelper.STAR_COLUMN)` -->
`isWildcard(expr)`?
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