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| <div class="title">Quantile<div class="ingroups"><a class="el" href="group__grp__deprecated.html">Deprecated Modules</a></div></div> </div> |
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| <dl class="section warning"><dt>Warning</dt><dd><em> This is an old implementation of quantile. Replacement of this function is available as built-in PERCENTILE_CONT in databases</em></dd></dl> |
| <div class="toc"><b>Contents</b> </p><ul> |
| <li> |
| <a href="#syntax">Function Syntax</a> </li> |
| <li> |
| <a href="#examples">Examples</a> </li> |
| <li> |
| <a href="#related">Related Topics</a> </li> |
| </ul> |
| </div><p>This module computes the specified quantile value. It reads the name of the table, the specific column, and computes the quantile value based on the fraction specified as the third argument.</p> |
| <p>For an implementation of quantile using sketches, check out the <a class="el" href="sketch_8sql__in.html#a2f2ab2fe3244515f5f73d49690e73b39" title="cmsketch_centile is a scalar UDF to compute a centile value from a cmsketch. Takes the results of the...">cmsketch_centile()</a> aggregate in the <a class="el" href="group__grp__countmin.html">CountMin (Cormode-Muthukrishnan)</a> module.</p> |
| <p><a class="anchor" id="syntax"></a></p><dl class="section user"><dt>Function Syntax</dt><dd></dd></dl> |
| <p>There are two implementations of quantile available depending on the size of the table.</p> |
| <p><a class="el" href="quantile_8sql__in.html#a6955e44659a0817803ab7a11a9a7e8a5" title="Computes quantile. ">quantile()</a> is best used for small tables (i.e., less than 5000 rows, with 1-2 columns in total).</p> |
| <pre class="syntax"> |
| quantile( table_name, |
| col_name, |
| quantile |
| ) |
| </pre><p>For larger tables, consider using <a class="el" href="quantile_8sql__in.html#a154435ddf6200110013dc05b1a6207fe" title="Computes quantile. ">quantile_big()</a> instead.</p> |
| <pre class="syntax"> |
| quantile_big( table_name, |
| col_name, |
| quantile |
| ) |
| </pre><p><a class="anchor" id="examples"></a></p><dl class="section user"><dt>Examples</dt><dd></dd></dl> |
| <ol type="1"> |
| <li>Prepare some input. <pre class="example"> |
| CREATE TABLE tab1 AS SELECT generate_series(1, 1000) AS col1; |
| </pre></li> |
| <li>Run the <a class="el" href="quantile_8sql__in.html#a6955e44659a0817803ab7a11a9a7e8a5" title="Computes quantile. ">quantile()</a> function. <pre class="example"> |
| SELECT quantile( 'tab1', |
| 'col1', |
| .3 |
| ); |
| </pre> Result: <pre class="result"> |
| quantile |
|  ------------- |
| 301.48046875 |
| (1 row) |
| </pre></li> |
| </ol> |
| <p>Note that this module is not available in HAWQ. GPDB 4.2+ and HAWQ 1.2+ support the SQL Standard percentile_cont() inverse distribution function which should be used preferentially to this implementation. It is also planned for support in Postgres 9.4. This implementation will be retired once the functionality is available in Postgres.</p> |
| <p><a class="anchor" id="related"></a></p><dl class="section user"><dt>Related Topics</dt><dd>File <a class="el" href="quantile_8sql__in.html" title="SQL function for Quantile. ">quantile.sql_in</a> documenting the SQL function.</dd></dl> |
| <p>Module <a class="el" href="group__grp__countmin.html">CountMin (Cormode-Muthukrishnan)</a> for an approximate quantile implementation. </p> |
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