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.rel.type.RelDataTypeFactory;
  import org.apache.calcite.rel.type.RelDataTypeField;
  import org.apache.calcite.sql.type.ArraySqlType;
  import org.apache.calcite.sql.type.MapSqlType;
  import org.apache.calcite.sql.type.MultisetSqlType;
  import org.apache.calcite.sql.type.OperandTypes;
  import org.apache.calcite.sql.type.SqlOperandCountRanges;
  import org.apache.calcite.sql.type.SqlTypeName;
  import org.apache.calcite.util.Util;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * The <code>UNNEST</code> operator.
   */
  public class SqlUnnestOperator extends SqlFunctionalOperator {
    /** Whether {@code WITH ORDINALITY} was specified.
     *
     * <p>If so, the returned records include a column {@code ORDINALITY}. */
    public final boolean withOrdinality;
  
    public static final String ORDINALITY_COLUMN_NAME = "ORDINALITY";
  
    public static final String MAP_KEY_COLUMN_NAME = "KEY";
  
    public static final String MAP_VALUE_COLUMN_NAME = "VALUE";
  
    //~ Constructors -----------------------------------------------------------
  
    public SqlUnnestOperator(boolean withOrdinality) {
      super(
          "UNNEST",
          SqlKind.UNNEST,
          200,
          true,
          null,
          null,
          OperandTypes.repeat(SqlOperandCountRanges.from(1),
              OperandTypes.SCALAR_OR_RECORD_COLLECTION_OR_MAP));
      this.withOrdinality = withOrdinality;
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public RelDataType inferReturnType(SqlOperatorBinding opBinding) {
      final RelDataTypeFactory typeFactory = opBinding.getTypeFactory();
      final RelDataTypeFactory.Builder builder = typeFactory.builder();
      for (Integer operand : Util.range(opBinding.getOperandCount())) {
        RelDataType type = opBinding.getOperandType(operand);
        if (type.getSqlTypeName() == SqlTypeName.ANY) {
          // Unnest Operator in schema less systems returns one column as the output
          // $unnest is a placeholder to specify that one column with type ANY is output.
          return builder
              .add("$unnest",
                  SqlTypeName.ANY)
              .nullable(true)
              .build();
        }
  
        if (type.isStruct()) {
          type = type.getFieldList().get(0).getType();
        }
  
        assert type instanceof ArraySqlType || type instanceof MultisetSqlType
            || type instanceof MapSqlType;
        // If a type is nullable, all field accesses inside the type are also nullable
        if (type instanceof MapSqlType) {
          MapSqlType mapType = (MapSqlType) type;
          builder.add(MAP_KEY_COLUMN_NAME, mapType.getKeyType());
          builder.add(MAP_VALUE_COLUMN_NAME, mapType.getValueType());
        } else {
          RelDataType componentType = requireNonNull(type.getComponentType(), "componentType");
          boolean isNullable = componentType.isNullable();
          if (!allowAliasUnnestItems(opBinding) && componentType.isStruct()) {
            for (RelDataTypeField field : componentType.getFieldList()) {
              RelDataType fieldType = field.getType();
              if (isNullable) {
                fieldType = typeFactory.enforceTypeWithNullability(fieldType, true);
              }
              builder.add(field.getName(), fieldType);
            }
          } else {
            builder.add(SqlUtil.deriveAliasFromOrdinal(operand),
                componentType);
          }
        }
      }
      if (withOrdinality) {
        builder.add(ORDINALITY_COLUMN_NAME, SqlTypeName.INTEGER);
      }
      return builder.build();
    }
  
    private static boolean allowAliasUnnestItems(SqlOperatorBinding operatorBinding) {
      return (operatorBinding instanceof SqlCallBinding)
          && ((SqlCallBinding) operatorBinding)
          .getValidator()
          .config()
          .conformance()
          .allowAliasUnnestItems();
    }
  
    @Override public void unparse(SqlWriter writer, SqlCall call, int leftPrec,
        int rightPrec) {
      super.unparse(writer, call, leftPrec, rightPrec);
      if (withOrdinality) {
        writer.keyword("WITH ORDINALITY");
      }
    }
  
    @Override public boolean argumentMustBeScalar(int ordinal) {
      return false;
    }
  
  }
  