feat: impl QueryEngine#execute, adds numbers table and query engine test (#13)

* feat: impl QueryEngine#execute, adds numbers table and query engine test

* fix: clippy warning

* fix: reuse runtime in context in table adapter

* fix: by CR comments

src/common/recordbatch/src/lib.rs

@@ -5,6 +5,7 @@ use std::pin::Pin;
 
 use datatypes::schema::SchemaRef;
 use error::Result;
+use futures::task::{Context, Poll};
 use futures::Stream;
 pub use recordbatch::RecordBatch;
 
@@ -13,3 +14,31 @@ pub trait RecordBatchStream: Stream<Item = Result<RecordBatch>> {
 }
 
 pub type SendableRecordBatchStream = Pin<Box<dyn RecordBatchStream + Send>>;
+
+/// EmptyRecordBatchStream can be used to create a RecordBatchStream
+/// that will produce no results
+pub struct EmptyRecordBatchStream {
+    /// Schema wrapped by Arc
+    schema: SchemaRef,
+}
+
+impl EmptyRecordBatchStream {
+    /// Create an empty RecordBatchStream
+    pub fn new(schema: SchemaRef) -> Self {
+        Self { schema }
+    }
+}
+
+impl RecordBatchStream for EmptyRecordBatchStream {
+    fn schema(&self) -> SchemaRef {
+        self.schema.clone()
+    }
+}
+
+impl Stream for EmptyRecordBatchStream {
+    type Item = Result<RecordBatch>;
+
+    fn poll_next(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(None)
+    }
+}