raminqaf commented on code in PR #28456:
URL: https://github.com/apache/flink/pull/28456#discussion_r3418412898
##########
docs/data/sql_functions.yml:
##########
@@ -1611,6 +1611,16 @@ aggregate:
`(NUMERIC: INTEGER_NUMERIC, FLOAT, DOUBLE, DECIMAL)`
Returns a `DOUBLE` if percentage is numeric, or an `ARRAY<DOUBLE>` if
percentage is an array. `NULL` if percentage is an empty array.
+ - sql: SINGLE_VALUE(expression)
+ description: |
+ Returns a single value of the expression within a group.
+
+ If the group contains more than one distinct value, an exception is
thrown at runtime.
+
+ E.g., SELECT SINGLE_VALUE(id) FROM T.
Review Comment:
If you don't define a aggregation you will face the exception
```
Caused by: org.apache.flink.table.api.TableRuntimeException:
SingleValueAggFunction received more than one element.
```
Try running this in
[WordCountSQLExample](https://github.com/raminqaf/flink/blob/b16909ae925fcee06ce11e73a7dc5ec24a7fadcf/flink-examples/flink-examples-table/src/main/java/org/apache/flink/table/examples/java/basics/WordCountSQLExample.java#L25-L25).
```suggestion
SELECT SINGLE_VALUE(word) AS single_val
FROM VALUES ('Hello'), ('Ciao'), ('World')
AS WordTable(word)
GROUP BY word
```
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