Github user JamesRTaylor commented on a diff in the pull request:
https://github.com/apache/incubator-phoenix/pull/30#discussion_r12076427
--- Diff:
phoenix-core/src/it/java/org/apache/phoenix/end2end/FirstByLastByFunctionIT.java
---
@@ -0,0 +1,557 @@
+/*
+ * Copyright 2014 The Apache Software Foundation
+ *
+ * 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.phoenix.end2end;
+
+import static org.junit.Assert.*;
+import java.sql.*;
+import org.junit.Test;
+
+/**
+ *
+ * @author tzolkincz
+ */
+public class FirstByLastByFunctionIT extends BaseHBaseManagedTimeIT {
+
+ private void prepareTable() throws Exception {
+ Connection conn = DriverManager.getConnection(getUrl());
+ String ddl = "CREATE TABLE IF NOT EXISTS firstBy "
+ + "(id INTEGER NOT NULL PRIMARY KEY, page_id
INTEGER,"
+ + " date INTEGER, \"value\" INTEGER)";
+ conn.createStatement().execute(ddl);
+
+ //in value column will be 0, 2, 4, 6, 8, so 8 is the biggest
+ for (int i = 0; i < 5; i++) {
+ conn.createStatement().execute("UPSERT INTO firstBy
(id, page_id, date, \"value\")"
+ + " VALUES (" + i + ", 8, " + 100 * i +
", " + i * 2 + ")");
+ }
+
+ conn.commit();
+ }
+
+ @Test
+ public void testFirst() throws Exception {
+ prepareTable();
+ Connection conn = DriverManager.getConnection(getUrl());
+
+ ResultSet rs = conn.createStatement().executeQuery(
+ "SELECT FIRST_BY(\"value\", date) FROM firstBy
GROUP BY page_id");
--- End diff --
True, we don't support these OLAP extensions yet, but in these cases, if
there's standard SQL syntax, we try to use it and support as much as we can. So
instead of calling the functions FIRST_BY and LAST_BY, we could call them
FIRST_VALUE and LAST_VALUE, not allow the PARTITION BY clause (since as you've
pointed out, we don't have support for this yet), but support the other parts
of the standard syntax like this:
FIRST_VALUE | LAST_VALUE
( expression ) OVER
( [ ORDER BY order_list ] )
Then we could support an NTH_VALUE function too, as above, but with the
additional argument you built-in allows:
NTH_VALUE
( expression, offset ) OVER
( [ ORDER BY order_list ] )
All of these are just the "syntax" - they'd all compile into the built-in
function you've implemented which wouldn't need to change. Both Oracle and
Postgres have this NTH_VALUE function:
http://www.postgresql.org/docs/8.4/static/functions-window.html
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