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| <h1 class="title topictitle1" id="ariaid-title1">Impala Aggregate Functions</h1> |
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| <div class="body conbody"> |
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| <p class="p"> |
| Aggregate functions are a special category with different rules. These functions |
| calculate a return value across all the items in a result set, so they require a |
| <code class="ph codeph">FROM</code> clause in the query: |
| </p> |
| |
| |
| <pre class="pre codeblock"><code>select count(product_id) from product_catalog; |
| select max(height), avg(height) from census_data where age > 20; |
| </code></pre> |
| |
| <p class="p"> |
| Aggregate functions also ignore <code class="ph codeph">NULL</code> values rather than returning a |
| <code class="ph codeph">NULL</code> result. For example, if some rows have <code class="ph codeph">NULL</code> for a |
| particular column, those rows are ignored when computing the <code class="ph codeph">AVG()</code> for |
| that column. Likewise, specifying <code class="ph codeph">COUNT(<var class="keyword varname">col_name</var>)</code> in |
| a query counts only those rows where <var class="keyword varname">col_name</var> contains a |
| non-<code class="ph codeph">NULL</code> value. |
| </p> |
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| <p class="p toc"></p> |
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| </div> |
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| <div class="related-links"> |
| <ul class="ullinks"> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_appx_median.html">APPX_MEDIAN Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_avg.html">AVG Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_count.html">COUNT Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_group_concat.html">GROUP_CONCAT Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_max.html">MAX Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_min.html">MIN Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_ndv.html">NDV Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_stddev.html">STDDEV, STDDEV_SAMP, STDDEV_POP Functions</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_sum.html">SUM Function</a></strong><br /> |
| </li> |
| <li class="link ulchildlink"><strong><a href="../topics/impala_variance.html">VARIANCE, VARIANCE_SAMP, VARIANCE_POP, VAR_SAMP, VAR_POP Functions</a></strong><br /> |
| </li> |
| </ul> |
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| <div class="familylinks"> |
| <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_functions.html">Impala Built-In Functions</a></div> |
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