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    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>System design</span> <!----></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Architecture</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TsFile</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>QueryEngine</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>SchemaManager</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>StorageEngine</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>DataQuery</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/SystemDesign/DataQuery/DataQuery.html" class="sidebar-link">DataQuery</a></li><li><a href="/SystemDesign/DataQuery/QueryFundamentals.html" class="sidebar-link">QueryFundamentals</a></li><li><a href="/SystemDesign/DataQuery/SeriesReader.html" class="sidebar-link">SeriesReader</a></li><li><a href="/SystemDesign/DataQuery/RawDataQuery.html" class="sidebar-link">RawDataQuery</a></li><li><a href="/SystemDesign/DataQuery/AggregationQuery.html" aria-current="page" class="active sidebar-link">AggregationQuery</a></li><li><a href="/SystemDesign/DataQuery/GroupByQuery.html" class="sidebar-link">GroupByQuery</a></li><li><a href="/SystemDesign/DataQuery/LastQuery.html" class="sidebar-link">LastQuery</a></li><li><a href="/SystemDesign/DataQuery/AlignByDeviceQuery.html" class="sidebar-link">AlignByDeviceQuery</a></li><li><a href="/SystemDesign/DataQuery/FillFunction.html" class="sidebar-link">FillFunction</a></li><li><a href="/SystemDesign/DataQuery/GroupByFillQuery.html" class="sidebar-link">GroupByFillQuery</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Tools</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Connector</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Client</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="content content__default"><h1 id="aggregation-query"><a href="#aggregation-query" class="header-anchor">#</a> Aggregation query</h1> <p>The main logic of the aggregation query is in AggregateExecutor</p> <ul><li>org.apache.iotdb.db.query.executor.AggregationExecutor</li></ul> <h2 id="aggregation-query-without-value-filter"><a href="#aggregation-query-without-value-filter" class="header-anchor">#</a> Aggregation query without value filter</h2> <p>For aggregate queries without value filters, the results are obtained by the <code>executeWithoutValueFilter()</code> method and a dataSet is constructed. First use the <code>mergeSameSeries()</code> method to merge aggregate queries for the same time series. For example: if you need to calculate count(s1), sum(s2), count(s3), sum(s1), you need to calculate two aggregation values of s1, then the pathToAggrIndexesMap result will be: s1-&gt; 0, 3; s2-&gt; 1; s3-&gt; 2.</p> <p>Then you will get <code>pathToAggrIndexesMap</code>, where each entry is an aggregate query of series, so you can calculate its aggregate value <code>aggregateResults</code> by calling the <code>groupAggregationsBySeries()</code> method.  Before you finally create the result set, you need to restore its order to the order of the user query.  Finally use the <code>constructDataSet()</code> method to create a result set and return it.</p> <p>The <code>groupAggregationsBySeries ()</code> method is explained in detail below.  First create an <code>IAggregateReader</code>:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IAggregateReader seriesReader = new SeriesAggregateReader(
        pathToAggrIndexes.getKey(), tsDataType, context, QueryResourceManager.getInstance()
        .getQueryDataSource(seriesPath, context, timeFilter), timeFilter, null);
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>For each entry (that is, series), first create an aggregate result <code>AggregateResult</code> for each aggregate query. Maintain a boolean list <code>isCalculatedList</code>, corresponding to whether each <code>AggregateResult</code> has been calculated. Record the remaining number of functions to be calculated in <code>remainingToCalculate</code>.  The list of boolean values and this count value will make some aggregate functions (such as <code>FIRST_VALUE</code>) not need to continue the entire loop process after obtaining the result.</p> <p>Next, update <code>AggregateResult</code> according to the usage method of <code>aggregateReader</code> introduced in Section 5.2:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>while (aggregateReader.hasNextChunk()) {
  if (aggregateReader.canUseCurrentChunkStatistics()) {
    Statistics chunkStatistics = aggregateReader.currentChunkStatistics();
    
    // do some aggregate calculation using chunk statistics
    ...
    
    aggregateReader.skipCurrentChunk();
    continue;
  }
	  
  while (aggregateReader.hasNextPage()) {
	 if (aggregateReader.canUseCurrentPageStatistics()) {
	   Statistics pageStatistic = aggregateReader.currentPageStatistics();
	   
	   // do some aggregate calculation using page statistics
      ...
	   
	   aggregateReader.skipCurrentPage();
	   continue;
	 } else {
	 	BatchData batchData = aggregateReader.nextPage();
	 	// do some aggregate calculation using batch data
      ...
	 }	 
  }
}
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br></div></div><p>It should be noted that before updating each result, you need to first determine whether it has been calculated (using the isCalculatedList list); after each update, call the isCalculatedAggregationResult () method to update the boolean values in the list  .  If all values in the list are true, that is, the value of <code>remainingToCalculate</code> is 0, it proves that all aggregate function results have been calculated and can be returned.</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>if (Boolean.FALSE.equals(isCalculatedList.get(i))) {
  AggregateResult aggregateResult = aggregateResultList.get(i);
  ... // update
  if (aggregateResult.isCalculatedAggregationResult()) {
    isCalculatedList.set(i, true);
    remainingToCalculate--;
    if (remainingToCalculate == 0) {
      return aggregateResultList;
    }
  }
}
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p>When using <code>overlapedPageData</code> to update, since each batch function result will traverse this batchData, you need to call the<code>resetBatchData ()</code>method to point the pointer to its starting position, so that the next function can traverse.</p> <h2 id="aggregated-query-with-value-filter"><a href="#aggregated-query-with-value-filter" class="header-anchor">#</a> Aggregated query with value filter</h2> <p>For an aggregate query with a value filter, obtain the results through the <code>executeWithoutValueFilter()</code> method and build a dataSet.  First create a <code>timestampGenerator</code> based on the expression, then create a <code>SeriesReaderByTimestamp</code> for each time series and place it in the <code>readersOfSelectedSeries</code> list; create an aggregate result for each query as <code>AggregateResult</code>, and place it in the <code>aggregateResults</code> list.</p> <p>After initialization is complete, call the <code>aggregateWithValueFilter()</code> method to update the result:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>while (timestampGenerator.hasNext()) {
  // Generate timestamps
  long[] timeArray = new long[aggregateFetchSize];
  int timeArrayLength = 0;
  for (int cnt = 0; cnt &lt; aggregateFetchSize; cnt++) {
    if (!timestampGenerator.hasNext()) {
      break;
    }
    timeArray[timeArrayLength++] = timestampGenerator.next();
  }

  // Calculate aggregate results using timestamps
  for (int i = 0; i &lt; readersOfSelectedSeries.size(); i++) {
    aggregateResults.get(i).updateResultUsingTimestamps(timeArray, timeArrayLength,
      readersOfSelectedSeries.get(i));
    }
  }
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br></div></div><h2 id="aggregated-query-with-level"><a href="#aggregated-query-with-level" class="header-anchor">#</a> Aggregated query with level</h2> <p>After aggregated query, we could also to count the total number of points of</p> <p>each node at the given level in current Metadata Tree.</p> <p>The logic is in the <code>AggregationExecutor</code> class.</p> <ol><li><p>In the beginning, get the final paths group by level and the origin path index to final path.</p> <blockquote><p>For example, we could get final path <code>root.sg1</code> by <code>root.sg1.d1.s0,root.sg1.d2.s1</code> and <code>level=1</code>.</p></blockquote></li> <li><p>Then, get the aggregated query result: RowRecord.</p></li> <li><p>Finally, merge each RowRecord to NewRecord, which has fields like &lt;final path, count&gt;.</p> <blockquote><p>For example, we will get new RowRecord <code>&lt;root.sg1,7&gt;</code> by <code>&lt;root.sg1.d1.s0, 3&gt;, &lt;root.sg1.d2.s1, 4&gt;</code> and level=1.</p></blockquote></li></ol> <blockquote><p>Attention:</p> <ol><li>only support count aggregation</li> <li>root's level == 0</li></ol></blockquote></div> <div class="page-nav"><p class="inner"><span class="prev">
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