implement sort merge join as a YProjector

with 2 separate upstream projectors to be used form different threads

sql/src/main/java/io/crate/operation/projectors/YProjector.java

@@ -0,0 +1,39 @@
+/*
+ * Licensed to CRATE Technology GmbH ("Crate") under one or more contributor
+ * license agreements.  See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.  Crate licenses
+ * this file to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.  You may
+ * obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * However, if you have executed another commercial license agreement
+ * with Crate these terms will supersede the license and you may use the
+ * software solely pursuant to the terms of the relevant commercial agreement.
+ */
+
+package io.crate.operation.projectors;
+
+/**
+ * Projector combining results from two sources, exposed via
+ * {@linkplain #leftProjector()} and {@linkplain #rightProjector()}.
+ */
+public interface YProjector {
+
+    /**
+     * initialize stuff here
+     */
+    public void startProjection();
+
+    public Projector leftProjector();
+
+    public Projector rightProjector();
+
+}

sql/src/main/java/io/crate/operation/projectors/join/RowCombinator.java

@@ -0,0 +1,32 @@
+/*
+ * Licensed to CRATE Technology GmbH ("Crate") under one or more contributor
+ * license agreements.  See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.  Crate licenses
+ * this file to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.  You may
+ * obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * However, if you have executed another commercial license agreement
+ * with Crate these terms will supersede the license and you may use the
+ * software solely pursuant to the terms of the relevant commercial agreement.
+ */
+
+package io.crate.operation.projectors.join;
+
+public class RowCombinator {
+
+    public static Object[] combineRow(Object[] innerRow, Object[] outerRow) {
+        Object[] newRow = new Object[outerRow.length + innerRow.length];
+        System.arraycopy(outerRow, 0, newRow, 0, outerRow.length);
+        System.arraycopy(innerRow, 0, newRow, outerRow.length, innerRow.length);
+        return newRow;
+    }
+}