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Druid adapter for Calcite
There is a newer version: 1.21.0.263
/*
 * 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.adapter.druid;

import org.apache.calcite.rel.type.RelDataType;
import org.apache.calcite.rex.RexCall;
import org.apache.calcite.rex.RexLiteral;
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.sql.SqlKind;
import org.apache.calcite.sql.SqlOperator;
import org.apache.calcite.sql.fun.SqlStdOperatorTable;

import javax.annotation.Nullable;

/**
 * Converts Calcite SUBSTRING call to Druid Expression when possible
 */
public class SubstringOperatorConversion implements DruidSqlOperatorConverter {
  @Override public SqlOperator calciteOperator() {
    return SqlStdOperatorTable.SUBSTRING;
  }

  @Nullable
  @Override public String toDruidExpression(RexNode rexNode, RelDataType rowType,
      DruidQuery query) {
    final RexCall call = (RexCall) rexNode;
    final String arg = DruidExpressions.toDruidExpression(
        call.getOperands().get(0), rowType, query);
    if (arg == null) {
      return null;
    }

    final String startIndex;
    final String length;
    // SQL is 1-indexed, Druid is 0-indexed.
    if (!call.getOperands().get(1).isA(SqlKind.LITERAL)) {
      final String arg1 = DruidExpressions.toDruidExpression(
          call.getOperands().get(1), rowType, query);
      if (arg1 == null) {
        // can not infer start index expression bailout.
        return null;
      }
      startIndex = DruidQuery.format("(%s - 1)", arg1);
    } else {
      startIndex = DruidExpressions.numberLiteral(
          RexLiteral.intValue(call.getOperands().get(1)) - 1);
    }

    if (call.getOperands().size() > 2) {
      //case substring from start index with length
      if (!call.getOperands().get(2).isA(SqlKind.LITERAL)) {
        // case it is an expression try to parse it
        length = DruidExpressions.toDruidExpression(
            call.getOperands().get(2), rowType, query);
        if (length == null) {
          return null;
        }
      } else {
        // case length is a constant
        length = DruidExpressions.numberLiteral(RexLiteral.intValue(call.getOperands().get(2)));
      }

    } else {
      //case substring from index to the end
      length = DruidExpressions.numberLiteral(-1);
    }
    return DruidQuery.format("substring(%s, %s, %s)", arg, startIndex, length);
  }
}

// End SubstringOperatorConversion.java