[GitHub] [spark] huaxingao commented on a change in pull request #28290: [MINOR][SQL][DOCS] Add a paragraph for scalar function in sql getting started

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huaxingao commented on a change in pull request #28290:
URL: https://github.com/apache/spark/pull/28290#discussion_r412681949



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File path: docs/sql-getting-started.md
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@@ -347,7 +347,8 @@ For example:
 </div>
 
 ## Scalar Functions
-(to be filled soon)
+
+Scalar functions are functions that return a single value per row, as opposed to aggregation functions, which return a value for a group of rows. Spark SQL supports a variety of built-in scalar functions such as [Array Functions](sql-ref-functions-builtin.html#array-functions), [Map Functions](sql-ref-functions-builtin.html#map-functions), [Date and Timestamp Functions](sql-ref-functions-builtin.html#date-and-timestamp-functions), etc. It also supports [User Defined Scalar Functions](sql-ref-functions-udf-scalar.html).

Review comment:
       I used Scalar function instead of built-in function (because the next paragraph is for aggregations). I don't want to talk about window function because I think window function is still sort of aggregation, even thought it returns result for each row.
   I can't link it to builtin function because builtin function contains aggregation function, so I link to each group of the builtin scalar functions. 




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