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;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.type.SqlOperandCountRanges;
  import org.apache.calcite.sql.type.SqlTypeName;
  import org.apache.calcite.sql.validate.SqlValidator;
  import org.apache.calcite.sql.validate.SqlValidatorScope;
  
  import static org.apache.calcite.util.Static.RESOURCE;
  
  /**
   * DESCRIPTOR appears as an argument in a function. DESCRIPTOR accepts a list of
   * identifiers that represent a list of names. The interpretation of names is left
   * to the function.
   *
   * <p>A typical syntax is DESCRIPTOR(col_name, ...).
   *
   * <p>An example is a table-valued function that takes names of columns to filter on.
   */
  public class SqlDescriptorOperator extends SqlOperator {
    public SqlDescriptorOperator() {
      super("DESCRIPTOR",
          SqlKind.DESCRIPTOR,
          100,
          100,
          opBinding -> opBinding.typeFactory.createSqlType(SqlTypeName.COLUMN_LIST),
          null,
          null);
    }
  
    @Override public RelDataType deriveType(
        SqlValidator validator,
        SqlValidatorScope scope, SqlCall call) {
      return validator.getTypeFactory().createSqlType(SqlTypeName.COLUMN_LIST);
    }
  
    @Override public boolean checkOperandTypes(
        SqlCallBinding callBinding,
        boolean throwOnFailure) {
      for (SqlNode operand : callBinding.getCall().getOperandList()) {
        if (!(operand instanceof SqlIdentifier)
            || ((SqlIdentifier) operand).isSimple()) {
          if (throwOnFailure) {
            throw SqlUtil.newContextException(operand.getParserPosition(),
                RESOURCE.aliasMustBeSimpleIdentifier());
          }
        }
      }
      return true;
    }
  
    @Override public SqlOperandCountRange getOperandCountRange() {
      return SqlOperandCountRanges.from(1);
    }
  
    @Override public SqlSyntax getSyntax() {
      return SqlSyntax.FUNCTION;
    }
  }
  