Github user jihoonson commented on a diff in the pull request:
https://github.com/apache/tajo/pull/422#discussion_r29862941
--- Diff:
tajo-plan/src/main/java/org/apache/tajo/plan/nameresolver/NameResolver.java ---
@@ -31,14 +34,30 @@
import org.apache.tajo.plan.verifier.VerifyException;
import org.apache.tajo.plan.logical.RelationNode;
import org.apache.tajo.util.Pair;
+import org.apache.tajo.util.StringUtils;
import org.apache.tajo.util.TUtil;
-import java.util.ArrayList;
+import java.util.Collection;
import java.util.List;
import java.util.Map;
+import java.util.Set;
/**
- * NameResolver utility
+ * Column name resolution utility. A SQL statement can include many kinds
of column names,
+ * defined in different ways. Some column name indicates just a column in
a relation.
+ * Another column name includes alias table name or alias column name,
derived from some expression.
+ *
+ * This utility ensures that each column name is derived from valid and
accessible column, and
+ * it also finds the exact data type of the column.
+ *
+ * Terminology:
+ * <ul>
+ * <li>Qualifier: database name, table name, or both included in a
column name</li>
+ * <li>Simple name: just column name without any qualifier</li>
--- End diff --
I have a question. When a column ```C``` has an alias ```A```, is its
simple name ```C``` or ```A```?
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