[GitHub] [spark] maropu commented on a change in pull request #28138: [SPARK-31366][DOCS][SQL] Add doc for the aggregation in SQL reference guide

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maropu commented on a change in pull request #28138: [SPARK-31366][DOCS][SQL] Add doc for the aggregation in SQL reference guide
URL: https://github.com/apache/spark/pull/28138#discussion_r404462684
 
 

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 File path: docs/sql-ref-syntax-qry-aggregation.md
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 @@ -19,4 +19,16 @@ license: |
   limitations under the License.
 ---
 
-**This page is under construction**
+
+An aggregate function operates on a group of rows and returns a single value.
+Spark supports various aggregations.
+Some examples of the common aggregation functions are <code>SUM</code>, <code>MIN</code>, <code>MAX</code> and <code>COUNT</code>.
+There are a rich set of aggregate functions that can be used along with the
+<code>GROUP BY</code> clause in <code>SELECT</code> queries.
+Spark also supports advanced aggregations using the <code>CUBE</code>, <code>GROUPING SETS</code> and <code>ROLLUP</code> clauses in <code>GROUP BY</code>.
+
+The following sections describe the query syntax and usage for the different aggregation functions.
+* [BUILT-IN AGGREGATE FUNCTIONS](sql-ref-functions-builtin-aggregate.html)
+* [CUBE](sql-ref-syntax-qry-select-groupby.html)
+* [GROUPING SETS](sql-ref-syntax-qry-select-groupby.html)
+* [ROLLUP](sql-ref-syntax-qry-select-groupby.html)
 
 Review comment:
   I feel this page to have many links to the same page is a bit verbose ... Actually, we need this page?

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