Github user shuxiong commented on a diff in the pull request:
https://github.com/apache/phoenix/pull/45#discussion_r26368458
--- Diff:
phoenix-core/src/main/java/org/apache/phoenix/expression/function/SignFunction.java
---
@@ -0,0 +1,85 @@
+/*
+ * 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.expression.function;
+
+import java.math.BigDecimal;
+import java.sql.SQLException;
+import java.util.List;
+
+import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
+import org.apache.phoenix.expression.Expression;
+import org.apache.phoenix.parse.FunctionParseNode.Argument;
+import org.apache.phoenix.parse.FunctionParseNode.BuiltInFunction;
+import org.apache.phoenix.schema.tuple.Tuple;
+import org.apache.phoenix.schema.types.PDataType;
+import org.apache.phoenix.schema.types.PDecimal;
+import org.apache.phoenix.schema.types.PNumericType;
+import org.apache.phoenix.schema.types.PRealNumber;
+import org.apache.phoenix.schema.types.PWholeNumber;
+
+/**
+ * Base class for built-in SIGN function.
+ * @since 4.3.0
+ */
+@BuiltInFunction(name = SignFunction.NAME,
+ args = { @Argument(allowedTypes = { PNumericType.class }) })
+public class SignFunction extends ScalarFunction {
+
+ public static final String NAME = "SIGN";
+
+ public SignFunction() {
+ }
+
+ public SignFunction(List<Expression> children) throws SQLException {
+ super(children);
+ }
+
+ @Override
+ public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {
+ Expression childExpr = children.get(0);
+ PDataType dataType = childExpr.getDataType();
+ if (childExpr.evaluate(tuple, ptr)) {
+ byte[] retBytes;
+ if (dataType instanceof PWholeNumber) {
--- End diff --
1) According to [1], signum's return type should be as same as argument
type.
2) Math#signum has a special case: it will return Nan, if the argument is
Nan.
So I choose to return different types for whole and real number.
When getting the result, we don't know its types. I come up with two ways
to construct the object,
1) try each type one by one, or
2) achieve as it is.
[1] http://www.postgresql.org/docs/current/static/functions-math.html
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