contrib/storage-jdbc/src/main/java/org/apache/drill/exec/store/jdbc/rules/JdbcLimitRule.java

/*
 * 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
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 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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 * See the License for the specific language governing permissions and
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package org.apache.drill.exec.store.jdbc.rules;

import org.apache.calcite.plan.RelTrait;
import org.apache.calcite.rel.RelCollations;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rex.RexLiteral;
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.sql.dialect.MssqlSqlDialect;
import org.apache.drill.exec.planner.common.DrillLimitRelBase;
import org.apache.drill.exec.store.enumerable.plan.DrillJdbcRuleBase;
import org.apache.drill.exec.store.enumerable.plan.DrillJdbcSort;
import org.apache.drill.exec.store.jdbc.DrillJdbcConvention;

import java.math.BigDecimal;
import java.util.Collections;

public class JdbcLimitRule extends DrillJdbcRuleBase.DrillJdbcLimitRule {
  private final DrillJdbcConvention convention;

  public JdbcLimitRule(RelTrait in, DrillJdbcConvention out) {
    super(in, out);
    this.convention = out;
  }

  @Override
  public RelNode convert(RelNode rel) {
    DrillLimitRelBase limit = (DrillLimitRelBase) rel;
    if (limit.getOffset() == null
      || !limit.getTraitSet().contains(RelCollations.EMPTY)
      || !(convention.dialect instanceof MssqlSqlDialect)) {
      return super.convert(limit);
    } else {
      // MS SQL doesn't support either OFFSET or FETCH without ORDER BY.
      // But for the case of FETCH without OFFSET, Calcite generates TOP N
      // instead of FETCH, and it is supported by MS SQL.
      // So do splitting the limit with both OFFSET and FETCH but without ORDER BY
      int offset = Math.max(0, RexLiteral.intValue(limit.getOffset()));
      int fetch = Math.max(0, RexLiteral.intValue(limit.getFetch()));

      // child Limit uses conservative approach: use offset 0 and fetch = parent limit offset + parent limit fetch.
      RexNode childFetch = limit.getCluster().getRexBuilder().makeExactLiteral(BigDecimal.valueOf(offset + fetch));

      RelNode jdbcSort = new DrillJdbcSort(limit.getCluster(), limit.getTraitSet().plus(RelCollations.EMPTY).replace(this.out).simplify(),
        convert(limit.getInput(), limit.getInput().getTraitSet().replace(this.out).simplify()),
        RelCollations.EMPTY, null, childFetch);

      return limit.copy(limit.getTraitSet(), Collections.singletonList(jdbcSort), true);
    }
  }
}