| /* |
| * 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.beam.sdk.extensions.sql.zetasql; |
| |
| import java.util.ArrayList; |
| import java.util.List; |
| import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rex.RexBuilder; |
| import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rex.RexNode; |
| import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.sql.SqlOperator; |
| import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.sql.fun.SqlStdOperatorTable; |
| import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.util.Util; |
| import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions; |
| import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.ImmutableList; |
| |
| /** |
| * Rewrites COALESCE calls as CASE ($case_no_value) calls. |
| * |
| * <p>Turns <code>COALESCE(a, b, c)</code> into: |
| * |
| * <pre><code>CASE |
| * WHEN a IS NOT NULL THEN a |
| * WHEN b IS NOT NULL THEN b |
| * ELSE c |
| * END</code></pre> |
| * |
| * <p>There is also a special case for the single-argument case: <code>COALESCE(a)</code> becomes |
| * just <code>a</code>. |
| */ |
| public class SqlCoalesceOperatorRewriter implements SqlOperatorRewriter { |
| @Override |
| public RexNode apply(RexBuilder rexBuilder, List<RexNode> operands) { |
| Preconditions.checkArgument( |
| operands.size() >= 1, "COALESCE should have at least one argument in function call."); |
| |
| // No need for a case operator if there's only one operand |
| if (operands.size() == 1) { |
| return operands.get(0); |
| } |
| |
| SqlOperator op = SqlStdOperatorTable.CASE; |
| |
| List<RexNode> newOperands = new ArrayList<>(); |
| for (RexNode operand : Util.skipLast(operands)) { |
| newOperands.add( |
| rexBuilder.makeCall(SqlStdOperatorTable.IS_NOT_NULL, ImmutableList.of(operand))); |
| newOperands.add(operand); |
| } |
| newOperands.add(Util.last(operands)); |
| |
| return rexBuilder.makeCall(op, newOperands); |
| } |
| } |