docs: add WITHIN GROUP for string_agg & array_agg (#1683)

Author: KKould

docs/en/sql-reference/20-sql-functions/07-aggregate-functions/aggregate-array-agg.md

@@ -8,7 +8,7 @@ The ARRAY_AGG function (also known by its alias LIST) transforms all the values,
 ## Syntax
 
 ```sql
-ARRAY_AGG(<expr>)
+ARRAY_AGG(<expr>) [ WITHIN GROUP ( <orderby_clause> ) ]
 
 LIST(<expr>)
 ```
@@ -19,6 +19,12 @@ LIST(<expr>)
 |-----------| -------------- |
 | `<expr>`  | Any expression |
 
+## Optional
+
+| Optional                            | Description                                           |
+|-------------------------------------|-------------------------------------------------------|
+| WITHIN GROUP [&lt;orderby_clause&gt;](https://docs.databend.com/sql/sql-commands/query-syntax/query-select#order-by-clause) | Defines the order of values in ordered set aggregates        |
+
 ## Return Type
 
 Returns an [Array](../../00-sql-reference/10-data-types/array.md) with elements that are of the same type as the original data.
@@ -52,4 +58,14 @@ GROUP BY movie_title;
 | movie_title |  ratings   |
 |-------------|------------|
 | Inception   | [5, 4, 5]  |
+
+-- List all ratings for Inception in an array Using `WITHIN GROUP`
+SELECT movie_title, ARRAY_AGG(rating) WITHIN GROUP ( ORDER BY rating DESC ) AS ratings
+FROM movie_ratings
+WHERE movie_title = 'Inception'
+GROUP BY movie_title;
+
+| movie_title |  ratings   |
+|-------------|------------|
+| Inception   | [5, 5, 4]  |
 ```

docs/en/sql-reference/20-sql-functions/07-aggregate-functions/aggregate-string-agg.md

@@ -4,13 +4,14 @@ title: STRING_AGG
 
 Aggregate function.
 
-The STRING_AGG() function converts all the non-NULL values of a column to String, separated by the delimiter.
+The STRING_AGG() function (also known as GROUP_CONCAT or LISTAGG) concatenates all the non-NULL values of a column to a string, separated by delimiter.
 
 ## Syntax
 
-```sql
-STRING_AGG(<expr>)
-STRING_AGG(<expr> [, delimiter])
+```sql 
+STRING_AGG(<expr> [, delimiter]) [ WITHIN GROUP ( <orderby_clause> ) ]
+GROUP_CONCAT(<expr> [, delimiter]) [ WITHIN GROUP ( <orderby_clause> ) ]
+LISTAGG(<expr> [, delimiter]) [ WITHIN GROUP ( <orderby_clause> ) ]
 ```
 
 :::info
@@ -32,7 +33,13 @@ SELECT string_agg(number::VARCHAR, '|') AS s FROM numbers(5);
 | Arguments   | Description                                                         |
 |-------------|---------------------------------------------------------------------|
 | `<expr>`    | Any string expression (if not a string, use `::VARCHAR` to convert) |
-| `delimiter` | Optional constant String, if not specified, use empty String        |
+
+## Optional
+
+| Optional                            | Description                                                  |
+|-------------------------------------|--------------------------------------------------------------|
+| `delimiter`                         | Optional constant String, if not specified, use empty String |
+| WITHIN GROUP [&lt;orderby_clause&gt;](https://docs.databend.com/sql/sql-commands/query-syntax/query-select#order-by-clause) | Defines the order of values in ordered set aggregates        |
 
 ## Return Type
 
@@ -64,8 +71,19 @@ FROM programming_languages;
 
 **Result**
 ```sql
-|          concatenated_languages         |
+|          concatenated_languages          |
 |------------------------------------------|
-| Python, JavaScript, Java, C#, Ruby      |
+| Python, JavaScript, Java, C#, Ruby       |
 ```
 
+**Query Demo: Concatenate Programming Language Names with a Delimiter Using `WITHIN GROUP`**
+```sql
+SELECT STRING_AGG(language_name, ', ') WITHIN GROUP ( ORDER BY language_name DESC ) AS concatenated_languages
+FROM programming_languages;
+```
+**Result**
+```sql
+|          concatenated_languages          |
+|------------------------------------------|
+| Ruby, Python, JavaScript, Java, C#       |
+```