Github user jihoonson commented on a diff in the pull request:
https://github.com/apache/tajo/pull/71#discussion_r15056936
--- Diff:
tajo-core/src/main/java/org/apache/tajo/engine/planner/nameresolver/NameResolvingMode.java
---
@@ -0,0 +1,80 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF 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.
+ */
+
+package org.apache.tajo.engine.planner.nameresolver;
+
+/**
+ *
+ * <h2>Motivation</h2>
+ *
+ * Please take a look at the following example query:
+ *
+ * <pre>
+ * select (l_orderkey + l_orderkey) l_orderkey from lineitem where
l_orderkey > 2 order by l_orderkey;
+ * </pre>
+ *
+ * Although <code>l_orderkey</code> seems to be ambiguous, the above
usages are available in commercial DBMSs.
+ * In order to eliminate the ambiguity, Tajo follows the behaviors of
PostgreSQL.
+ *
+ * <h2>Resolving Modes</h2>
+ *
+ * From the behaviors of PostgreSQL, we found that there are three kinds
of name resolving modes.
+ * Each definition is as follows:
+ *
+ * <ul>
+ * <li><b>RELS_ONLY</b> finds a column from the relations in the current
block.
+ * <li><b>RELS_AND_SUBEXPRS</b> finds a column from the all relations in
the current block and
+ * from aliased temporal fields; a temporal field means an explicitly
aliased expression. If there are duplicated
+ * columns in the relation and temporal fields, this level firstly
chooses the field in a relation.</li>
+ * <li><b>SUBEXPRS_AND_RELS</b> is very similar to
<code>RELS_AND_SUBEXPRS</code>. The main difference is that it
+ * firstly chooses an aliased temporal field instead of the fields in a
relation.</li>
+ * </ul>
+ *
+ * <h2>The relationship between resolving modes and operators</h3>
+ *
+ * <ul>
+ * <li>fields in select list are resolved in the REL_ONLY mode.</li>
+ * <li>fields in WHERE clause are resolved in the RELS_AND_SUBEXPRS
mode.</li>
+ * <li>fields in GROUP BY, HAVING, ORDER BY, and LIMIT are resolved in
the SUBEXPRS_AND_RELS mode.</li>
--- End diff --
As you commented, fields in LIMIT are resolved in the REL_ONLY mode. Please
fix it.
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