[GitHub] [incubator-druid] gianm commented on a change in pull request #8814: SQL: Add RAND() function.

[GitBox <gi...@apache.org>]

gianm commented on a change in pull request #8814: SQL: Add RAND() function.
URL: https://github.com/apache/incubator-druid/pull/8814#discussion_r343292920
 
 

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 File path: processing/src/main/java/org/apache/druid/query/expression/RandExprMacro.java
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 @@ -0,0 +1,95 @@
+/*
+ * 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.druid.query.expression;
+
+import com.google.common.collect.Iterables;
+import org.apache.druid.java.util.common.IAE;
+import org.apache.druid.math.expr.Expr;
+import org.apache.druid.math.expr.ExprEval;
+import org.apache.druid.math.expr.ExprMacroTable;
+import org.apache.druid.segment.DimensionHandlerUtils;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Random;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.function.DoubleSupplier;
+
+public class RandExprMacro implements ExprMacroTable.ExprMacro
+{
+  @Override
+  public String name()
+  {
+    return "rand";
+  }
+
+  @Override
+  public Expr apply(List<Expr> args)
+  {
+    final DoubleSupplier randomGenerator;
+
+    if (args.isEmpty()) {
+      randomGenerator = () -> ThreadLocalRandom.current().nextDouble();
+    } else if (args.size() == 1) {
+      final Expr seedArg = Iterables.getOnlyElement(args);
+      if (seedArg.isLiteral()) {
+        final Long seedValue = DimensionHandlerUtils.convertObjectToLong(seedArg.getLiteralValue());
+        if (seedValue != null) {
+          final Random random = new Random(seedValue);
+          randomGenerator = random::nextDouble;
+        } else {
+          throw new IAE("Function[%s] first argument must be a number literal");
+        }
+      } else {
+        throw new IAE("Function[%s] first argument must be a number literal");
+      }
+    } else {
+      throw new IAE("Function[%s] needs zero or one arguments", name());
+    }
+
+    class RandExpr extends ExprMacroTable.BaseScalarMacroFunctionExpr
 
 Review comment:
   It's sort of the same thing as an anonymous class, except it's not anonymous. I use them somewhat interchangeably. I'm not aware of any major advantage except that the class name is nicer in stack traces, debuggers, etc.

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