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Lu, Huayi e6fa411af0 DWS DEV 830.201 version 
Reviewed-by: Pruthi, Vineet <vineet.pruthi@t-systems.com>
Co-authored-by: Lu, Huayi <luhuayi@huawei.com>
Co-committed-by: Lu, Huayi <luhuayi@huawei.com>
2024-05-16 07:24:04 +00:00

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<a name="EN-US_TOPIC_0000001233708675"></a><a name="EN-US_TOPIC_0000001233708675"></a>
<h1 class="topictitle1">HLL Data Types</h1>
<div id="body1551855680017"><p id="EN-US_TOPIC_0000001233708675__p266653594010">HyperLoglog (HLL) is an approximation algorithm for efficiently counting the number of distinct values in a data set. It features faster computing and lower space usage. You only need to store HLL data structures, instead of data sets. When new data is added to a data set, make hash calculation on the data and insert the result to an HLL. Then, you can obtain the final result based on the HLL.</p>
<p id="EN-US_TOPIC_0000001233708675__p6598153041113"><a href="#EN-US_TOPIC_0000001233708675__table55621821164213">Table 1</a> compares HLL with other algorithms.</p>
<div class="tablenoborder"><a name="EN-US_TOPIC_0000001233708675__table55621821164213"></a><a name="table55621821164213"></a><table cellpadding="4" cellspacing="0" summary="" id="EN-US_TOPIC_0000001233708675__table55621821164213" frame="border" border="1" rules="all"><caption><b>Table 1 </b>Comparison between HLL and other algorithms</caption><thead align="left"><tr id="EN-US_TOPIC_0000001233708675__row145621215428"><th align="left" class="cellrowborder" valign="top" width="25%" id="mcps1.3.3.2.5.1.1"><p id="EN-US_TOPIC_0000001233708675__p1956242111428">Item</p>
</th>
<th align="left" class="cellrowborder" valign="top" width="25%" id="mcps1.3.3.2.5.1.2"><p id="EN-US_TOPIC_0000001233708675__p9562102104217">Sorting Algorithm</p>
</th>
<th align="left" class="cellrowborder" valign="top" width="25%" id="mcps1.3.3.2.5.1.3"><p id="EN-US_TOPIC_0000001233708675__p135625217421">Hash Algorithm</p>
</th>
<th align="left" class="cellrowborder" valign="top" width="25%" id="mcps1.3.3.2.5.1.4"><p id="EN-US_TOPIC_0000001233708675__p2562192111427">HLL</p>
</th>
</tr>
</thead>
<tbody><tr id="EN-US_TOPIC_0000001233708675__row1562321194214"><td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.1 "><p id="EN-US_TOPIC_0000001233708675__p556217217422">Time complexity</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.2 "><p id="EN-US_TOPIC_0000001233708675__p55621321114210">O(nlogn)</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.3 "><p id="EN-US_TOPIC_0000001233708675__p1556272113423">O(n)</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.4 "><p id="EN-US_TOPIC_0000001233708675__p95621821184211">O(n)</p>
</td>
</tr>
<tr id="EN-US_TOPIC_0000001233708675__row356262120427"><td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.1 "><p id="EN-US_TOPIC_0000001233708675__p16562142124210">Space complexity</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.2 "><p id="EN-US_TOPIC_0000001233708675__p1056282119429">O(n)</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.3 "><p id="EN-US_TOPIC_0000001233708675__p956202117427">O(n)</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.4 "><p id="EN-US_TOPIC_0000001233708675__p18562102134215">1280 bytes</p>
</td>
</tr>
<tr id="EN-US_TOPIC_0000001233708675__row195621221144216"><td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.1 "><p id="EN-US_TOPIC_0000001233708675__p92131078457">Error rate</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.2 "><p id="EN-US_TOPIC_0000001233708675__p16562102117426">0</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.3 "><p id="EN-US_TOPIC_0000001233708675__p956242112421">0</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.4 "><p id="EN-US_TOPIC_0000001233708675__p1956212124216">≈2%</p>
</td>
</tr>
<tr id="EN-US_TOPIC_0000001233708675__row156262112426"><td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.1 "><p id="EN-US_TOPIC_0000001233708675__p20562182184218">Storage space requirement</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.2 "><p id="EN-US_TOPIC_0000001233708675__p15624217424">Size of raw data</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.3 "><p id="EN-US_TOPIC_0000001233708675__p185621621174219">Size of raw data</p>
</td>
<td class="cellrowborder" valign="top" width="25%" headers="mcps1.3.3.2.5.1.4 "><p id="EN-US_TOPIC_0000001233708675__p1656252110421">1280 bytes</p>
</td>
</tr>
</tbody>
</table>
</div>
<p id="EN-US_TOPIC_0000001233708675__p3344104752112">HLL has advantages over others in the computing speed and storage space requirement. In terms of time complexity, the sorting algorithm needs O(nlogn) time for sorting, and the hash algorithm and HLL need O(n) time for full table scanning. In terms of storage space requirements, the sorting algorithm and hash algorithm need to store raw data before collecting statistics, whereas the HLL algorithm needs to store only the HLL data structures rather than the raw data, and thereby occupying a fixed space of only 1280 bytes.</p>
<div class="notice" id="EN-US_TOPIC_0000001233708675__nefb03bb3bc3b43ebab25400e08dd3c02"><span class="noticetitle"><img src="public_sys-resources/notice_3.0-en-us.png"> </span><div class="noticebody"><ul id="EN-US_TOPIC_0000001233708675__u2b9b4bd9065b4bbab9d39720b62ab4bc"><li id="EN-US_TOPIC_0000001233708675__li209183912584">In default specifications, the maximum number of distinct values is 1.6e plus 12, and the maximum error rate is only 2.3%. If a calculation result exceeds the maximum number, the error rate of the calculation result will increase, or the calculation will fail and an error will be reported.</li><li id="EN-US_TOPIC_0000001233708675__ld9cc546ab654416c8a7fb0ae98c6f0b3">When using this feature for the first time, you need to evaluate the distinct values of the service, properly select configuration parameters, and perform verification to ensure that the accuracy meets requirements.<ul id="EN-US_TOPIC_0000001233708675__ul47111736112220"><li id="EN-US_TOPIC_0000001233708675__li289333120229">When default parameter configuration is used, the calculated number of distinct values is 1.6e plus 12. If the calculated result is <strong id="EN-US_TOPIC_0000001233708675__b638973412437">NaN</strong>, you need to adjust <strong id="EN-US_TOPIC_0000001233708675__b8851201114415">log2m</strong> and <strong id="EN-US_TOPIC_0000001233708675__b5600161684411">regwidth</strong> to accommodate more distinct values.</li><li id="EN-US_TOPIC_0000001233708675__li20894183142217">The hash algorithm has an extremely low probability of collision. However, you are still advised to select 2 or 3 hash seeds for verification when using the hash algorithm for the first time. If there is only a small difference between the distinct values, you can select any one of the seeds as the hash seed.</li></ul>
</li></ul>
</div></div>
<p id="EN-US_TOPIC_0000001233708675__p5743051103"><a href="#EN-US_TOPIC_0000001233708675__table18186113885012">Table 2</a> describes main HLL data structures.</p>
<div class="tablenoborder"><a name="EN-US_TOPIC_0000001233708675__table18186113885012"></a><a name="table18186113885012"></a><table cellpadding="4" cellspacing="0" summary="" id="EN-US_TOPIC_0000001233708675__table18186113885012" frame="border" border="1" rules="all"><caption><b>Table 2 </b>Main HLL data structures</caption><thead align="left"><tr id="EN-US_TOPIC_0000001233708675__row161861538145014"><th align="left" class="cellrowborder" valign="top" width="25.28%" id="mcps1.3.7.2.3.1.1"><p id="EN-US_TOPIC_0000001233708675__p17186123895020">Data Type</p>
</th>
<th align="left" class="cellrowborder" valign="top" width="74.72%" id="mcps1.3.7.2.3.1.2"><p id="EN-US_TOPIC_0000001233708675__p01861938115013">Description</p>
</th>
</tr>
</thead>
<tbody><tr id="EN-US_TOPIC_0000001233708675__row4186133819508"><td class="cellrowborder" valign="top" width="25.28%" headers="mcps1.3.7.2.3.1.1 "><p id="EN-US_TOPIC_0000001233708675__p19186153811502">hll</p>
</td>
<td class="cellrowborder" valign="top" width="74.72%" headers="mcps1.3.7.2.3.1.2 "><p id="EN-US_TOPIC_0000001233708675__p818613818508">Its size is always 1280 bytes, which can be directly used to calculate the number of distinct values.</p>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="EN-US_TOPIC_0000001233708675__section1873615258196"><h4 class="sectiontitle">Application Scenarios of HLL</h4><ul id="EN-US_TOPIC_0000001233708675__ul355014315272"><li id="EN-US_TOPIC_0000001233708675__li355023112274">Using the HLL Data Type<ol id="EN-US_TOPIC_0000001233708675__ol16682192311272"><li id="EN-US_TOPIC_0000001233708675__li868212312720">Create an HLL table and insert an empty HLL into the table.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen3311164562419"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">helloworld</span><span class="w"> </span><span class="p">(</span><span class="n">id</span><span class="w"> </span><span class="nb">integer</span><span class="p">,</span><span class="w"> </span><span class="k">set</span><span class="w"> </span><span class="n">hll</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">helloworld</span><span class="p">(</span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="k">set</span><span class="p">)</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">hll_empty</span><span class="p">());</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li5683423142712">Add an integer that has gone through hash calculation into to the HLL.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen38531517263"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">UPDATE</span><span class="w"> </span><span class="n">helloworld</span><span class="w"> </span><span class="k">SET</span><span class="w"> </span><span class="k">set</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">hll_add</span><span class="p">(</span><span class="k">set</span><span class="p">,</span><span class="w"> </span><span class="n">hll_hash_integer</span><span class="p">(</span><span class="mi">12345</span><span class="p">))</span><span class="w"> </span><span class="k">WHERE</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li56832230272">Add a string that has gone through hash calculation into to the HLL.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen3238111272519"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">UPDATE</span><span class="w"> </span><span class="n">helloworld</span><span class="w"> </span><span class="k">SET</span><span class="w"> </span><span class="k">set</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">hll_add</span><span class="p">(</span><span class="k">set</span><span class="p">,</span><span class="w"> </span><span class="n">hll_hash_text</span><span class="p">(</span><span class="s1">'hello world'</span><span class="p">))</span><span class="w"> </span><span class="k">WHERE</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li6683223162719">Obtain the number of distinct values of the HLL.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen916913371260"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">hll_cardinality</span><span class="p">(</span><span class="k">set</span><span class="p">)</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">helloworld</span><span class="w"> </span><span class="k">WHERE</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
<span class="w"> </span><span class="n">hll_cardinality</span><span class="w"> </span>
<span class="c1">-----------------</span>
<span class="w"> </span><span class="mi">2</span>
<span class="p">(</span><span class="mi">1</span><span class="w"> </span><span class="k">row</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ol>
</li><li id="EN-US_TOPIC_0000001233708675__li461668142918">Using HLL to Collect Website Visitor Statistics<ol id="EN-US_TOPIC_0000001233708675__ol747015233214"><li id="EN-US_TOPIC_0000001233708675__li19470029329">Create the original data table <strong id="EN-US_TOPIC_0000001233708675__b995319421879">facts</strong> to record the time when a user accesses a website.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen12828540123216"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="p">(</span>
<span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="nb">date</span><span class="p">,</span>
<span class="w"> </span><span class="n">user_id</span><span class="w"> </span><span class="nb">integer</span>
<span class="p">);</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li193319914332">Insert user visits data.<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen939119993318"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span>
<span class="normal">6</span>
<span class="normal">7</span>
<span class="normal">8</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-20'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">100</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-21'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">200</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-22'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">300</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-23'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">400</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-24'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">500</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-25'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">600</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-26'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">700</span><span class="p">));</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">facts</span><span class="w"> </span><span class="k">VALUES</span><span class="w"> </span><span class="p">(</span><span class="s1">'2019-02-27'</span><span class="p">,</span><span class="w"> </span><span class="n">generate_series</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">800</span><span class="p">));</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li937124443512">Create another table and specify an HLL column: Group data by date and insert the data into the HLL:<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen59773302358"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span>
<span class="normal">6</span>
<span class="normal">7</span>
<span class="normal">8</span>
<span class="normal">9</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">daily_uniques</span><span class="w"> </span><span class="p">(</span>
<span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="k">UNIQUE</span><span class="p">,</span>
<span class="w"> </span><span class="n">users</span><span class="w"> </span><span class="n">hll</span>
<span class="p">);</span>
<span class="w"> </span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">daily_uniques</span><span class="p">(</span><span class="nb">date</span><span class="p">,</span><span class="w"> </span><span class="n">users</span><span class="p">)</span>
<span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="nb">date</span><span class="p">,</span><span class="w"> </span><span class="n">hll_add_agg</span><span class="p">(</span><span class="n">hll_hash_integer</span><span class="p">(</span><span class="n">user_id</span><span class="p">))</span>
<span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">facts</span>
<span class="w"> </span><span class="k">GROUP</span><span class="w"> </span><span class="k">BY</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li1039264812352">Calculate the numbers of users visiting the website every day:<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen13444182283412"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="nb">date</span><span class="p">,</span><span class="w"> </span><span class="n">hll_cardinality</span><span class="p">(</span><span class="n">users</span><span class="p">)</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">daily_uniques</span><span class="w"> </span><span class="k">ORDER</span><span class="w"> </span><span class="k">BY</span><span class="w"> </span><span class="nb">date</span><span class="p">;</span>
<span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">hll_cardinality</span><span class="w"> </span>
<span class="c1">---------------------+------------------</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">20</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">100</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">21</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">203</span><span class="p">.</span><span class="mi">813355588808</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">22</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">308</span><span class="p">.</span><span class="mi">048239950384</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">23</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">410</span><span class="p">.</span><span class="mi">529188080374</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">24</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">513</span><span class="p">.</span><span class="mi">263875705319</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">25</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">609</span><span class="p">.</span><span class="mi">271181107416</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">26</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">702</span><span class="p">.</span><span class="mi">941844662509</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">27</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">792</span><span class="p">.</span><span class="mi">249946595237</span>
<span class="p">(</span><span class="mi">8</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li187418399499">Calculate the number of users who had visited the website in the week from February 20, 2019 to February 26, 2019:<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen4937134915337"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">hll_cardinality</span><span class="p">(</span><span class="n">hll_union_agg</span><span class="p">(</span><span class="n">users</span><span class="p">))</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">daily_uniques</span><span class="w"> </span><span class="k">WHERE</span><span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="s1">'2019-02-20'</span><span class="p">::</span><span class="nb">date</span><span class="w"> </span><span class="k">AND</span><span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="s1">'2019-02-26'</span><span class="p">::</span><span class="nb">date</span><span class="p">;</span>
<span class="w"> </span><span class="n">hll_cardinality</span><span class="w"> </span>
<span class="c1">------------------</span>
<span class="w"> </span><span class="mi">702</span><span class="p">.</span><span class="mi">941844662509</span>
<span class="p">(</span><span class="mi">1</span><span class="w"> </span><span class="k">row</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li><li id="EN-US_TOPIC_0000001233708675__li1170255884913">Calculate the number of users who had visited the website yesterday but have not visited the website today:<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen124611836153317"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="nb">date</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="o">#</span><span class="n">hll_union_agg</span><span class="p">(</span><span class="n">users</span><span class="p">)</span><span class="w"> </span><span class="n">OVER</span><span class="w"> </span><span class="n">two_days</span><span class="p">)</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">#</span><span class="n">users</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="n">lost_uniques</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">daily_uniques</span><span class="w"> </span><span class="n">WINDOW</span><span class="w"> </span><span class="n">two_days</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="p">(</span><span class="k">ORDER</span><span class="w"> </span><span class="k">BY</span><span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="k">ASC</span><span class="w"> </span><span class="k">ROWS</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="n">PRECEDING</span><span class="p">);</span><span class="w"> </span>
<span class="w"> </span><span class="nb">date</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">lost_uniques</span><span class="w"> </span>
<span class="c1">---------------------+--------------</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">20</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">21</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">22</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">23</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">24</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">25</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">26</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="w"> </span><span class="mi">2019</span><span class="o">-</span><span class="mi">02</span><span class="o">-</span><span class="mi">27</span><span class="w"> </span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mi">00</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span>
<span class="p">(</span><span class="mi">8</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
</li></ol>
</li><li id="EN-US_TOPIC_0000001233708675__li6135333152920">HLL Format Errors<p id="EN-US_TOPIC_0000001233708675__p161481942195218"><a name="EN-US_TOPIC_0000001233708675__li6135333152920"></a><a name="li6135333152920"></a>When inserting data into a column of the HLL type, ensure that the data meets the requirements of the HLL data structure. If the data does not meet the requirements after being parsed, an error will be reported.</p>
<p id="EN-US_TOPIC_0000001233708675__p182299479366">For example, when <strong id="EN-US_TOPIC_0000001233708675__b512585411310">E\\1234'</strong> is inserted, the data does not comply with the HLL data structure and cannot be parsed. As a result, an error is reported.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001233708675__screen022920474366"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">test</span><span class="p">(</span><span class="n">id</span><span class="w"> </span><span class="nb">integer</span><span class="p">,</span><span class="w"> </span><span class="k">set</span><span class="w"> </span><span class="n">hll</span><span class="p">);</span>
<span class="k">INSERT</span><span class="w"> </span><span class="k">INTO</span><span class="w"> </span><span class="n">test</span><span class="w"> </span><span class="k">VALUES</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="s1">'E\\1234'</span><span class="p">);</span>
<span class="n">ERROR</span><span class="p">:</span><span class="w"> </span><span class="n">invalid</span><span class="w"> </span><span class="k">input</span><span class="w"> </span><span class="n">syntax</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nb">integer</span><span class="p">:</span><span class="w"> </span><span class="ss">&quot;E\\1234&quot;</span>
</pre></div></td></tr></table></div>
</div>
</li></ul>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="dws_06_0008.html">Data Types</a></div>
</div>
</div>
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