content: /*
   * 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.calcite.sql.fun;
  
  import org.apache.calcite.sql.SqlCall;
  import org.apache.calcite.sql.SqlFunction;
  import org.apache.calcite.sql.SqlFunctionCategory;
  import org.apache.calcite.sql.SqlKind;
  import org.apache.calcite.sql.SqlLiteral;
  import org.apache.calcite.sql.SqlNode;
  import org.apache.calcite.sql.SqlNodeList;
  import org.apache.calcite.sql.parser.SqlParserPos;
  import org.apache.calcite.sql.type.OperandTypes;
  import org.apache.calcite.sql.type.ReturnTypes;
  import org.apache.calcite.sql.validate.SqlValidator;
  
  import java.util.List;
  
  /**
   * The <code>NULLIF</code> function.
   */
  public class SqlNullifFunction extends SqlFunction {
    //~ Constructors -----------------------------------------------------------
  
    public SqlNullifFunction() {
      // NOTE jvs 26-July-2006:  We fill in the type strategies here,
      // but normally they are not used because the validator invokes
      // rewriteCall to convert NULLIF into CASE early.  However,
      // validator rewrite can optionally be disabled, in which case these
      // strategies are used.
      super("NULLIF",
          SqlKind.NULLIF,
          ReturnTypes.ARG0_FORCE_NULLABLE,
          null,
          OperandTypes.COMPARABLE_UNORDERED_COMPARABLE_UNORDERED,
          SqlFunctionCategory.SYSTEM);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    // override SqlOperator
    @Override public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
      List<SqlNode> operands = call.getOperandList();
      SqlParserPos pos = call.getParserPosition();
  
      checkOperandCount(
          validator,
          getOperandTypeChecker(),
          call);
      assert operands.size() == 2;
  
      SqlNodeList whenList = new SqlNodeList(pos);
      SqlNodeList thenList = new SqlNodeList(pos);
      whenList.add(operands.get(1));
      thenList.add(SqlLiteral.createNull(SqlParserPos.ZERO));
      return SqlCase.createSwitched(pos, operands.get(0), whenList, thenList,
          SqlNode.clone(operands.get(0)));
    }
  }
  