Java Code Examples for org.apache.calcite.sql.SqlLiteral#createBoolean()

/** @see #dispatch */
public Result visit(Correlate e) {
  final Result leftResult =
      visitChild(0, e.getLeft())
          .resetAlias(e.getCorrelVariable(), e.getRowType());
  parseCorrelTable(e, leftResult);
  final Result rightResult = visitChild(1, e.getRight());
  final SqlNode rightLateral =
      SqlStdOperatorTable.LATERAL.createCall(POS, rightResult.node);
  final SqlNode rightLateralAs =
      SqlStdOperatorTable.AS.createCall(POS, rightLateral,
          new SqlIdentifier(rightResult.neededAlias, POS));

  final SqlNode join =
      new SqlJoin(POS,
          leftResult.asFrom(),
          SqlLiteral.createBoolean(false, POS),
          JoinType.COMMA.symbol(POS),
          rightLateralAs,
          JoinConditionType.NONE.symbol(POS),
          null);
  return result(join, leftResult, rightResult);
}
 

public Result visitJoin(Join e) {
  final Result leftResult = visitChild(0, e.getLeft());
  final Result rightResult = visitChild(1, e.getRight());
  final Context leftContext = leftResult.qualifiedContext();
  final Context rightContext =
      rightResult.qualifiedContext();
  SqlNode sqlCondition = convertConditionToSqlNode(e.getCondition(),
      leftContext,
      rightContext,
      e.getLeft().getRowType().getFieldCount());
  SqlNode join =
      new SqlJoin(POS,
          leftResult.asFrom(),
          SqlLiteral.createBoolean(false, POS),
          joinType(e.getJoinType()).symbol(POS),
          rightResult.asFrom(),
          JoinConditionType.ON.symbol(POS),
          sqlCondition);
  return result(join, leftResult, rightResult);
}
 

/** @see #dispatch */
public Result visit(Join e) {
  final Result leftResult = visitChild(0, e.getLeft()).resetAlias();
  final Result rightResult = visitChild(1, e.getRight()).resetAlias();
  final Context leftContext = leftResult.qualifiedContext();
  final Context rightContext = rightResult.qualifiedContext();
  SqlNode sqlCondition = null;
  SqlLiteral condType = JoinConditionType.ON.symbol(POS);
  JoinType joinType = joinType(e.getJoinType());
  if (isCrossJoin(e)) {
    joinType = dialect.emulateJoinTypeForCrossJoin();
    condType = JoinConditionType.NONE.symbol(POS);
  } else {
    sqlCondition = convertConditionToSqlNode(e.getCondition(),
        leftContext,
        rightContext,
        e.getLeft().getRowType().getFieldCount());
  }
  SqlNode join =
      new SqlJoin(POS,
          leftResult.asFrom(),
          SqlLiteral.createBoolean(false, POS),
          joinType.symbol(POS),
          rightResult.asFrom(),
          condType,
          sqlCondition);
  return result(join, leftResult, rightResult);
}
 

public SqlCall createCall(
    SqlLiteral functionQualifier,
    SqlParserPos pos,
    SqlNode... operands) {
  pos = pos.plusAll(Arrays.asList(operands));
  operands = Arrays.copyOf(operands, operands.length + 1);
  operands[operands.length - 1] = SqlLiteral.createBoolean(caseSensitive, SqlParserPos.ZERO);
  return new SqlBasicCall(this, operands, pos, false, functionQualifier);
}
 

/** @see #dispatch */
public Result visit(Join e) {
  if (e.getJoinType() == JoinRelType.ANTI || e.getJoinType() == JoinRelType.SEMI) {
    return visitAntiOrSemiJoin(e);
  }
  final Result leftResult = visitChild(0, e.getLeft()).resetAlias();
  final Result rightResult = visitChild(1, e.getRight()).resetAlias();
  final Context leftContext = leftResult.qualifiedContext();
  final Context rightContext = rightResult.qualifiedContext();
  SqlNode sqlCondition = null;
  SqlLiteral condType = JoinConditionType.ON.symbol(POS);
  JoinType joinType = joinType(e.getJoinType());
  if (isCrossJoin(e)) {
    joinType = dialect.emulateJoinTypeForCrossJoin();
    condType = JoinConditionType.NONE.symbol(POS);
  } else {
    sqlCondition = convertConditionToSqlNode(e.getCondition(),
        leftContext,
        rightContext,
        e.getLeft().getRowType().getFieldCount(),
        dialect);
  }
  SqlNode join =
      new SqlJoin(POS,
          leftResult.asFrom(),
          SqlLiteral.createBoolean(false, POS),
          joinType.symbol(POS),
          rightResult.asFrom(),
          condType,
          sqlCondition);
  return result(join, leftResult, rightResult);
}
 

private SqlCall toSql(RexProgram program, RexOver rexOver) {
  final RexWindow rexWindow = rexOver.getWindow();
  final SqlNodeList partitionList = new SqlNodeList(
      toSql(program, rexWindow.partitionKeys), POS);

  List<SqlNode> orderNodes = Expressions.list();
  if (rexWindow.orderKeys != null) {
    for (RexFieldCollation rfc : rexWindow.orderKeys) {
      addOrderItem(orderNodes, program, rfc);
    }
  }
  final SqlNodeList orderList =
      new SqlNodeList(orderNodes, POS);

  final SqlLiteral isRows =
      SqlLiteral.createBoolean(rexWindow.isRows(), POS);

  // null defaults to true.
  // During parsing the allowPartial == false (e.g. disallow partial)
  // is expand into CASE expression and is handled as a such.
  // Not sure if we can collapse this CASE expression back into
  // "disallow partial" and set the allowPartial = false.
  final SqlLiteral allowPartial = null;

  SqlAggFunction sqlAggregateFunction = rexOver.getAggOperator();

  SqlNode lowerBound = null;
  SqlNode upperBound = null;

  if (sqlAggregateFunction.allowsFraming()) {
    lowerBound = createSqlWindowBound(rexWindow.getLowerBound());
    upperBound = createSqlWindowBound(rexWindow.getUpperBound());
  }

  final SqlWindow sqlWindow = SqlWindow.create(null, null, partitionList,
      orderList, isRows, lowerBound, upperBound, allowPartial, POS);

  final List<SqlNode> nodeList = toSql(program, rexOver.getOperands());
  return createOverCall(sqlAggregateFunction, nodeList, sqlWindow);
}
 

/**
 * @see #dispatch
 */
@Override
public SqlImplementor.Result visit(Join e) {
  final DremioRelToSqlConverter.Result leftResult = (DremioRelToSqlConverter.Result) visitChild(0, e.getLeft()).resetAlias();
  final DremioRelToSqlConverter.Result rightResult = (DremioRelToSqlConverter.Result) visitChild(1, e.getRight()).resetAlias();

  SqlNode sqlCondition = null;
  SqlLiteral condType = JoinConditionType.ON.symbol(POS);
  JoinType joinType = joinType(e.getJoinType());
  final Context leftContext = leftResult.qualifiedContext();
  final Context rightContext = rightResult.qualifiedContext();
  final Context joinContext = leftContext.implementor().joinContext(leftContext, rightContext);
  final RexNode condition = e.getCondition() == null ?
    null :
    this.simplifyDatetimePlus(e.getCondition(), e.getCluster().getRexBuilder());
  sqlCondition = joinContext.toSql(null, condition);

  final SqlNode join =
    new SqlJoin(POS,
      leftResult.asFrom(),
      SqlLiteral.createBoolean(false, POS),
      joinType.symbol(POS),
      rightResult.asFrom(),
      condType,
      sqlCondition);
  return result(join, leftResult, rightResult);
}
 

/**
 * @see #dispatch
 */
public Result visit(Join e) {
  final Result leftResult = visitChild(0, e.getLeft()).resetAlias();
  final Result rightResult = visitChild(1, e.getRight()).resetAlias();
  final Context leftContext = leftResult.qualifiedContext();
  final Context rightContext = rightResult.qualifiedContext();
  SqlNode sqlCondition = null;
  SqlLiteral condType = JoinConditionType.ON.symbol(POS);
  JoinType joinType = joinType(e.getJoinType());
  if (e.getJoinType() == JoinRelType.INNER && e.getCondition().isAlwaysTrue()) {
    joinType = JoinType.COMMA;
    condType = JoinConditionType.NONE.symbol(POS);
  } else {
    final RexNode condition = e.getCondition() != null
      ? simplifyDatetimePlus(e.getCondition(), e.getCluster().getRexBuilder())
      : null;
    sqlCondition = convertConditionToSqlNode(
      condition,
      leftContext,
      rightContext,
      e.getLeft().getRowType().getFieldCount());
  }
  SqlNode join =
    new SqlJoin(POS,
      leftResult.asFrom(),
      SqlLiteral.createBoolean(false, POS),
      joinType.symbol(POS),
      rightResult.asFrom(),
      condType,
      sqlCondition);
  return result(join, leftResult, rightResult);
}
 

protected SqlCall toSql(RexProgram program, RexOver rexOver) {
  final RexWindow rexWindow = rexOver.getWindow();
  final SqlNodeList partitionList = new SqlNodeList(
    toSql(program, rexWindow.partitionKeys), POS);

  ImmutableList.Builder<SqlNode> orderNodes = ImmutableList.builder();
  if (rexWindow.orderKeys != null) {
    for (RexFieldCollation rfc : rexWindow.orderKeys) {
      orderNodes.add(toSql(program, rfc));
    }
  }
  final SqlNodeList orderList =
    new SqlNodeList(orderNodes.build(), POS);

  final SqlLiteral isRows =
    SqlLiteral.createBoolean(rexWindow.isRows(), POS);

  final SqlNode lowerBound =
    createSqlWindowBound(rexWindow.getLowerBound());
  final SqlNode upperBound =
    createSqlWindowBound(rexWindow.getUpperBound());

  // null defaults to true.
  // During parsing the allowPartial == false (e.g. disallow partial)
  // is expand into CASE expression and is handled as a such.
  // Not sure if we can collapse this CASE expression back into
  // "disallow partial" and set the allowPartial = false.
  final SqlLiteral allowPartial = null;

  final SqlWindow sqlWindow = SqlWindow.create(null, null, partitionList,
    orderList, isRows, lowerBound, upperBound, allowPartial, POS);

  final List<SqlNode> nodeList = toSql(program, rexOver.getOperands());
  final SqlCall aggFunctionCall =
    rexOver.getAggOperator().createCall(POS, nodeList);

  return SqlStdOperatorTable.OVER.createCall(POS, aggFunctionCall,
    sqlWindow);
}
 

public static SqlCreateReflection createRaw(SqlParserPos pos, SqlIdentifier tblName, SqlNodeList displayList,
                                            SqlNodeList distributionList, SqlNodeList partitionList,
                                            SqlNodeList sortList,
                                            PartitionDistributionStrategy partitionDistributionStrategy,
                                            SqlIdentifier name) {
  return new SqlCreateReflection(pos, tblName, SqlLiteral.createBoolean(true, SqlParserPos.ZERO), displayList, null, null,
      distributionList, partitionList, sortList, partitionDistributionStrategy, name);
}
 

public static SqlCreateReflection createAggregation(SqlParserPos pos, SqlIdentifier tblName, SqlNodeList dimensionList,
                                                    SqlNodeList measureList, SqlNodeList distributionList,
                                                    SqlNodeList partitionList, SqlNodeList sortList,
                                                    PartitionDistributionStrategy partitionDistributionStrategy, SqlIdentifier name) {
  return new SqlCreateReflection(pos, tblName, SqlLiteral.createBoolean(false, SqlParserPos.ZERO), null, dimensionList,
      measureList, distributionList, partitionList, sortList, partitionDistributionStrategy, name);
}
 

private SqlCall toSql(RexProgram program, RexOver rexOver) {
    final RexWindow rexWindow = rexOver.getWindow();
    final SqlNodeList partitionList = new SqlNodeList(toSql(program, rexWindow.partitionKeys), POS);

    ImmutableList.Builder<SqlNode> orderNodes = ImmutableList.builder();
    if (rexWindow.orderKeys != null) {
        for (RexFieldCollation rfc : rexWindow.orderKeys) {
            orderNodes.add(toSql(program, rfc));
        }
    }
    final SqlNodeList orderList = new SqlNodeList(orderNodes.build(), POS);

    final SqlLiteral isRows = SqlLiteral.createBoolean(rexWindow.isRows(), POS);

    // null defaults to true.
    // During parsing the allowPartial == false (e.g. disallow partial)
    // is expand into CASE expression and is handled as a such.
    // Not sure if we can collapse this CASE expression back into
    // "disallow partial" and set the allowPartial = false.
    final SqlLiteral allowPartial = null;

    SqlAggFunction sqlAggregateFunction = rexOver.getAggOperator();

    SqlNode lowerBound = null;
    SqlNode upperBound = null;

    if (sqlAggregateFunction.allowsFraming()) {
        lowerBound = createSqlWindowBound(rexWindow.getLowerBound());
        upperBound = createSqlWindowBound(rexWindow.getUpperBound());
    }

    final SqlWindow sqlWindow = SqlWindow.create(null, null, partitionList, orderList, isRows, lowerBound,
            upperBound, allowPartial, POS);

    final List<SqlNode> nodeList = toSql(program, rexOver.getOperands());
    return createOverCall(sqlAggregateFunction, nodeList, sqlWindow);
}
 

@Override
public SqlCall toSql(RexProgram program, RexOver rexOver) {
  final RexWindow rexWindow = rexOver.getWindow();
  final SqlNodeList partitionList = new SqlNodeList(
    toSql(program, rexWindow.partitionKeys), POS);

  ImmutableList.Builder<SqlNode> orderNodes = ImmutableList.builder();
  if (rexWindow.orderKeys != null) {
    for (RexFieldCollation rfc : rexWindow.orderKeys) {
      // Omit ORDER BY <ordinal> clauses, which are parsed by Calcite but not actually
      // used for sorting.
      if (!(rfc.getKey() instanceof RexLiteral)) {
        if (rfc.getNullDirection() != dialect.defaultNullDirection(rfc.getDirection())) {
          // Get the SQL Node for the column being sorted on only.
          final SqlNode orderingColumnNode = toSql(program, rfc.left);

          final SqlNode emulatedNullDirNode = dialect.emulateNullDirection(orderingColumnNode,
            rfc.getNullDirection() == RelFieldCollation.NullDirection.FIRST, rfc.getDirection().isDescending());
          if (emulatedNullDirNode != null) {
            // Dialect requires emulating null direction.
            // Put the emulation in the order list first, then the ordering on the column only.
            orderNodes.add(emulatedNullDirNode);
            orderNodes.add(orderingColumnNode);
          } else {
            // Dialect implements NULLS FIRST and NULLS LAST clauses. These will get
            // unparsed as part of the RexFieldCollation.
            orderNodes.add(toSql(program, rfc));
          }
        } else {
          orderNodes.add(toSql(program, rfc));
        }
      }
    }
  }

  final SqlNodeList orderList =
    new SqlNodeList(orderNodes.build(), POS);

  final SqlLiteral isRows =
    SqlLiteral.createBoolean(rexWindow.isRows(), POS);

  final SqlNode lowerBound;
  final SqlNode upperBound;

  // Remove unnecessary Window Frames. When Calcite parses an OVER clause with no frame,
  final boolean hasUnnecessaryFrame = getDialect().removeDefaultWindowFrame(rexOver)
    && OverUtils.hasDefaultFrame(rexOver);

  if (hasUnnecessaryFrame) {
    lowerBound = null;
    upperBound = null;
  } else {
    lowerBound = createSqlWindowBound(rexWindow.getLowerBound());
    upperBound = createSqlWindowBound(rexWindow.getUpperBound());
  }

  // null defaults to true.
  // During parsing the allowPartial == false (e.g. disallow partial)
  // is expand into CASE expression and is handled as a such.
  // Not sure if we can collapse this CASE expression back into
  // "disallow partial" and set the allowPartial = false.
  final SqlLiteral allowPartial = null;

  final SqlWindow sqlWindow = getDremioRelToSqlConverter().adjustWindowForSource(
    this, rexOver.getAggOperator(), SqlWindow.create(
      null, null, partitionList,
      orderList, isRows, lowerBound, upperBound, allowPartial, POS));

  final List<SqlNode> nodeList = toSql(program, rexOver.getOperands());

  // Create the call for the aggregate in the window function.
  // If it happens to be a SUM0 call, we need to swap that with our own version which sets
  // the name to just SUM, rather than $SUM0, so that it can be translated to SQL compatible
  // with RDBMSes.
  final SqlAggFunction operator = rexOver.getAggOperator() != SqlStdOperatorTable.SUM0 ?
    rexOver.getAggOperator() : SUM0_FUNCTION;

  final SqlCall aggFunctionCall = operator.createCall(POS, nodeList);

  return SqlStdOperatorTable.OVER.createCall(POS, aggFunctionCall,
    sqlWindow);
}
 

public List<SqlNode> toSql(Window.Group group, ImmutableList<RexLiteral> constants,
                           int inputFieldCount) {
  final List<SqlNode> rexOvers = new ArrayList<>();
  final List<SqlNode> partitionKeys = new ArrayList<>();
  final List<SqlNode> orderByKeys = new ArrayList<>();
  for (int partition : group.keys) {
    partitionKeys.add(this.field(partition));
  }
  for (RelFieldCollation collation : group.orderKeys.getFieldCollations()) {
    this.addOrderItem(orderByKeys, collation);
  }
  SqlLiteral isRows = SqlLiteral.createBoolean(group.isRows, POS);
  SqlNode lowerBound = null;
  SqlNode upperBound = null;

  final SqlLiteral allowPartial = null;

  for (Window.RexWinAggCall winAggCall : group.aggCalls) {
    SqlAggFunction aggFunction = (SqlAggFunction) winAggCall.getOperator();
    final SqlWindow sqlWindow = SqlWindow.create(null, null,
      new SqlNodeList(partitionKeys, POS), new SqlNodeList(orderByKeys, POS),
      isRows, lowerBound, upperBound, allowPartial, POS);
    if (aggFunction.allowsFraming()) {
      lowerBound = createSqlWindowBound(group.lowerBound);
      upperBound = createSqlWindowBound(group.upperBound);
      sqlWindow.setLowerBound(lowerBound);
      sqlWindow.setUpperBound(upperBound);
    }

    RexShuttle replaceConstants = new RexShuttle() {
      @Override
      public RexNode visitInputRef(RexInputRef inputRef) {
        int index = inputRef.getIndex();
        RexNode ref;
        if (index > inputFieldCount - 1) {
          ref = constants.get(index - inputFieldCount);
        } else {
          ref = inputRef;
        }
        return ref;
      }
    };
    RexCall aggCall = (RexCall) winAggCall.accept(replaceConstants);
    List<SqlNode> operands = toSql(null, aggCall.operands);
    rexOvers.add(createOverCall(aggFunction, operands, sqlWindow));
  }
  return rexOvers;
}
 

public List<SqlNode> toSql(Window.Group group, ImmutableList<RexLiteral> constants,
    int inputFieldCount) {
  final List<SqlNode> rexOvers = new ArrayList<>();
  final List<SqlNode> partitionKeys = new ArrayList<>();
  final List<SqlNode> orderByKeys = new ArrayList<>();
  for (int partition: group.keys) {
    partitionKeys.add(this.field(partition));
  }
  for (RelFieldCollation collation: group.orderKeys.getFieldCollations()) {
    this.addOrderItem(orderByKeys, collation);
  }
  SqlLiteral isRows = SqlLiteral.createBoolean(group.isRows, POS);
  SqlNode lowerBound = null;
  SqlNode upperBound = null;

  final SqlLiteral allowPartial = null;

  for (Window.RexWinAggCall winAggCall: group.aggCalls) {
    SqlAggFunction aggFunction = (SqlAggFunction) winAggCall.getOperator();
    final SqlWindow sqlWindow = SqlWindow.create(null, null,
            new SqlNodeList(partitionKeys, POS), new SqlNodeList(orderByKeys, POS),
            isRows, lowerBound, upperBound, allowPartial, POS);
    if (aggFunction.allowsFraming()) {
      lowerBound = createSqlWindowBound(group.lowerBound);
      upperBound = createSqlWindowBound(group.upperBound);
      sqlWindow.setLowerBound(lowerBound);
      sqlWindow.setUpperBound(upperBound);
    }

    RexShuttle replaceConstants = new RexShuttle() {
      @Override public RexNode visitInputRef(RexInputRef inputRef) {
        int index = inputRef.getIndex();
        RexNode ref;
        if (index > inputFieldCount - 1) {
          ref = constants.get(index - inputFieldCount);
        } else {
          ref = inputRef;
        }
        return ref;
      }
    };
    RexCall aggCall = (RexCall) winAggCall.accept(replaceConstants);
    List<SqlNode> operands = toSql(null, aggCall.operands);
    rexOvers.add(createOverCall(aggFunction, operands, sqlWindow));
  }
  return rexOvers;
}
 

public SqlNode convertLiteral(RexLiteral literal) {
  // Numeric
  if (SqlTypeFamily.EXACT_NUMERIC.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createExactNumeric(
        literal.getValue().toString(),
        SqlParserPos.ZERO);
  }

  if (SqlTypeFamily.APPROXIMATE_NUMERIC.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createApproxNumeric(
        literal.getValue().toString(),
        SqlParserPos.ZERO);
  }

  // Timestamp
  if (SqlTypeFamily.TIMESTAMP.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createTimestamp(
        literal.getValueAs(TimestampString.class),
        0,
        SqlParserPos.ZERO);
  }

  // Date
  if (SqlTypeFamily.DATE.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createDate(
        literal.getValueAs(DateString.class),
        SqlParserPos.ZERO);
  }

  // Time
  if (SqlTypeFamily.TIME.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createTime(
        literal.getValueAs(TimeString.class),
        0,
        SqlParserPos.ZERO);
  }

  // String
  if (SqlTypeFamily.CHARACTER.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createCharString(
        ((NlsString) (literal.getValue())).getValue(),
        SqlParserPos.ZERO);
  }

  // Boolean
  if (SqlTypeFamily.BOOLEAN.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createBoolean(
        (Boolean) literal.getValue(),
        SqlParserPos.ZERO);
  }

  // Null
  if (SqlTypeFamily.NULL == literal.getTypeName().getFamily()) {
    return SqlLiteral.createNull(SqlParserPos.ZERO);
  }

  return null;
}
 

public SqlNode convertLiteral(RexLiteral literal) {
  // Numeric
  if (SqlTypeFamily.EXACT_NUMERIC.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createExactNumeric(
        literal.getValue().toString(),
        SqlParserPos.ZERO);
  }

  if (SqlTypeFamily.APPROXIMATE_NUMERIC.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createApproxNumeric(
        literal.getValue().toString(),
        SqlParserPos.ZERO);
  }

  // Timestamp
  if (SqlTypeFamily.TIMESTAMP.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createTimestamp(
        literal.getValueAs(TimestampString.class),
        0,
        SqlParserPos.ZERO);
  }

  // Date
  if (SqlTypeFamily.DATE.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createDate(
        literal.getValueAs(DateString.class),
        SqlParserPos.ZERO);
  }

  // Time
  if (SqlTypeFamily.TIME.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createTime(
        literal.getValueAs(TimeString.class),
        0,
        SqlParserPos.ZERO);
  }

  // String
  if (SqlTypeFamily.CHARACTER.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createCharString(
        ((NlsString) (literal.getValue())).getValue(),
        SqlParserPos.ZERO);
  }

  // Boolean
  if (SqlTypeFamily.BOOLEAN.getTypeNames().contains(
      literal.getTypeName())) {
    return SqlLiteral.createBoolean(
        (Boolean) literal.getValue(),
        SqlParserPos.ZERO);
  }

  // Null
  if (SqlTypeFamily.NULL == literal.getTypeName().getFamily()) {
    return SqlLiteral.createNull(SqlParserPos.ZERO);
  }

  return null;
}