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| <p>SQL functions for sketch-based approximations of descriptive statistics. |
| <a href="#details">More...</a></p> |
| |
| <p><a href="sketch_8sql__in_source.html">Go to the source code of this file.</a></p> |
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| <tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a> |
| Functions</h2></td></tr> |
| <tr class="memitem:a5a7e077028d5e0441552a77db3586db1"><td class="memItemLeft" align="right" valign="top">aggregate int8 </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a5a7e077028d5e0441552a77db3586db1">fmsketch_dcount</a> (anyelement column)</td></tr> |
| <tr class="memdesc:a5a7e077028d5e0441552a77db3586db1"><td class="mdescLeft"> </td><td class="mdescRight">Flajolet-Martin's distinct count estimation. <a href="#a5a7e077028d5e0441552a77db3586db1">More...</a><br/></td></tr> |
| <tr class="separator:a5a7e077028d5e0441552a77db3586db1"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:a323b932332f2db302469f14dc5fae369"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a323b932332f2db302469f14dc5fae369"></a> |
| aggregate text </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a323b932332f2db302469f14dc5fae369">cmsketch</a> (int8 column)</td></tr> |
| <tr class="memdesc:a323b932332f2db302469f14dc5fae369"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch</code> is a UDA that can be run on columns of type int8, or any column that can be cast to an int8. It produces a base64 string representing a CountMin sketch: a large array of counters that is intended to be passed into a UDF like <code>cmsketch_width_histogram</code> described below. <br/></td></tr> |
| <tr class="separator:a323b932332f2db302469f14dc5fae369"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:a3498d2c778d1289154f61d34e84c609e"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a3498d2c778d1289154f61d34e84c609e"></a> |
| int8 </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a3498d2c778d1289154f61d34e84c609e">cmsketch_count</a> (text sketches64, int8 val)</td></tr> |
| <tr class="memdesc:a3498d2c778d1289154f61d34e84c609e"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch_count</code> is a scalar UDF to compute the approximate number of occurences of a value in a column summarized by a cmsketch. Takes the results of the <code>cmsketch</code> aggregate as its first argument, and the desired value as the second. <br/></td></tr> |
| <tr class="separator:a3498d2c778d1289154f61d34e84c609e"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:aeff9e36cfb3338c4e405d4ac77d3968c"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="aeff9e36cfb3338c4e405d4ac77d3968c"></a> |
| int8 </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#aeff9e36cfb3338c4e405d4ac77d3968c">cmsketch_rangecount</a> (text sketches64, int8 bot, int8 top)</td></tr> |
| <tr class="memdesc:aeff9e36cfb3338c4e405d4ac77d3968c"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch_rangecount</code> is a scalar UDF to approximate the number of occurrences of values in the range <code>[lo,hi]</code> inclusive, given a cmsketch of a column. Takes the results of the <code>cmsketch</code> aggregate as its first argument, and the desired range boundaries as the second and third. <br/></td></tr> |
| <tr class="separator:aeff9e36cfb3338c4e405d4ac77d3968c"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:a2f2ab2fe3244515f5f73d49690e73b39"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a2f2ab2fe3244515f5f73d49690e73b39"></a> |
| int8 </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a2f2ab2fe3244515f5f73d49690e73b39">cmsketch_centile</a> (text sketches64, int8 centile, int8 cnt)</td></tr> |
| <tr class="memdesc:a2f2ab2fe3244515f5f73d49690e73b39"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch_centile</code> is a scalar UDF to compute a centile value from a cmsketch. Takes the results of the <code>cmsketch</code> aggregate as its first argument, a number between 1 and 99 as the desired centile in the second, and the count of the column as the third. Produces a value from the sketched column that is approximately at the centile's position in sorted order. <br/></td></tr> |
| <tr class="separator:a2f2ab2fe3244515f5f73d49690e73b39"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:a0ef6428fa7ba4b7f7b1f633e6f8003ea"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a0ef6428fa7ba4b7f7b1f633e6f8003ea"></a> |
| int8 </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a0ef6428fa7ba4b7f7b1f633e6f8003ea">cmsketch_median</a> (text sketches64, int8 cnt)</td></tr> |
| <tr class="memdesc:a0ef6428fa7ba4b7f7b1f633e6f8003ea"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch_median</code> is a scalar UDF to compute a median value from a cmsketch. Takes the results of the <code>cmsketch</code> aggregate as its first argument, and the count as the second. Produces a value from the sketched column that is approximately at the halfway position in sorted order. <br/></td></tr> |
| <tr class="separator:a0ef6428fa7ba4b7f7b1f633e6f8003ea"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:a8482f62849adf40a2c7df78c23ea33a4"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a8482f62849adf40a2c7df78c23ea33a4"></a> |
| text </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a8482f62849adf40a2c7df78c23ea33a4">cmsketch_width_histogram</a> (text sketches64, int8 themin, int8 themax, int4 nbuckets)</td></tr> |
| <tr class="memdesc:a8482f62849adf40a2c7df78c23ea33a4"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch_width_histogram</code> is a scalar UDF that takes three aggregates of a column – cmsketch, min and max– as well as a number of buckets, and produces an n-bucket histogram for the column where each bucket has approximately the same width. The output is a text string containing triples {lo, hi, count} representing the buckets; counts are approximate. <br/></td></tr> |
| <tr class="separator:a8482f62849adf40a2c7df78c23ea33a4"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:a9e6d30f20b724b96249cc4a0f67a279e"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="a9e6d30f20b724b96249cc4a0f67a279e"></a> |
| text </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#a9e6d30f20b724b96249cc4a0f67a279e">cmsketch_depth_histogram</a> (text sketches64, int4 nbuckets)</td></tr> |
| <tr class="memdesc:a9e6d30f20b724b96249cc4a0f67a279e"><td class="mdescLeft"> </td><td class="mdescRight"><code>cmsketch_depth_histogram</code> is a UDA that takes a cmsketch and a number of buckets n, and produces an n-bucket histogram for the column where each bucket has approximately the same count. The output is a text string containing triples {lo, hi, count} representing the buckets; counts are approximate. Note that an equi-depth histogram is equivalent to a spanning set of equi-spaced centiles. <br/></td></tr> |
| <tr class="separator:a9e6d30f20b724b96249cc4a0f67a279e"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:ab915f092b747e3a955cbb699afc9c70c"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="ab915f092b747e3a955cbb699afc9c70c"></a> |
| aggregate text[][] </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#ab915f092b747e3a955cbb699afc9c70c">mfvsketch_top_histogram</a> (anyelement column, int4 number_of_buckets)</td></tr> |
| <tr class="memdesc:ab915f092b747e3a955cbb699afc9c70c"><td class="mdescLeft"> </td><td class="mdescRight">Produces an n-bucket histogram for a column where each bucket counts one of the most frequent values in the column. The output is an array of doubles {value, count} in descending order of frequency; counts are approximated via CountMin sketches. Ties are handled arbitrarily. <br/></td></tr> |
| <tr class="separator:ab915f092b747e3a955cbb699afc9c70c"><td class="memSeparator" colspan="2"> </td></tr> |
| <tr class="memitem:ac5923758586e5203e80895526d3e561f"><td class="memItemLeft" align="right" valign="top"><a class="anchor" id="ac5923758586e5203e80895526d3e561f"></a> |
| aggregate text[][] </td><td class="memItemRight" valign="bottom"><a class="el" href="sketch_8sql__in.html#ac5923758586e5203e80895526d3e561f">mfvsketch_quick_histogram</a> (anyelement column, int4 number_of_buckets)</td></tr> |
| <tr class="memdesc:ac5923758586e5203e80895526d3e561f"><td class="mdescLeft"> </td><td class="mdescRight">On Postgres it works the same way as <a class="el" href="sketch_8sql__in.html#ab915f092b747e3a955cbb699afc9c70c">mfvsketch_top_histogram</a> but, in Greenplum it does parallel aggregation to provide a "quick and dirty" answer. <br/></td></tr> |
| <tr class="separator:ac5923758586e5203e80895526d3e561f"><td class="memSeparator" colspan="2"> </td></tr> |
| </table> |
| <a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2> |
| <div class="textblock"><dl class="section date"><dt>Date</dt><dd>April 2011</dd></dl> |
| <dl class="section see"><dt>See Also</dt><dd>For a brief introduction to sketches, see the module description <a class="el" href="group__grp__sketches.html">Sketch-based Estimators</a> </dd></dl> |
| |
| <p>Definition in file <a class="el" href="sketch_8sql__in_source.html">sketch.sql_in</a>.</p> |
| </div><h2 class="groupheader">Function Documentation</h2> |
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| <td class="memname">aggregate int8 fmsketch_dcount </td> |
| <td>(</td> |
| <td class="paramtype">anyelement </td> |
| <td class="paramname"><em>column</em>)</td><td></td> |
| <td></td> |
| </tr> |
| </table> |
| </div><div class="memdoc"> |
| <dl class="params"><dt>Parameters</dt><dd> |
| <table class="params"> |
| <tr><td class="paramname">column</td><td>name </td></tr> |
| </table> |
| </dd> |
| </dl> |
| |
| <p>Definition at line <a class="el" href="sketch_8sql__in_source.html#l00313">313</a> of file <a class="el" href="sketch_8sql__in_source.html">sketch.sql_in</a>.</p> |
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