SQL: [Docs] Add limitation for aggregate functions on scalars
Currently aggregate functions can operate only directly on fields.
They cannot be used on top of scalar functions as painless scripting
is currently not supported.
@@ -70,6 +70,12 @@ When doing aggregations (`GROUP BY`) {es-sql} relies on {es}'s `composite` aggre
But this type of aggregation does come with a limitation: sorting can only be applied on the key used for the aggregation's buckets. This
means that queries like `SELECT * FROM test GROUP BY age ORDER BY COUNT(*)` are not possible.
+[float]
+=== Using aggregation functions on top of scalar functions
+
+Aggregation functions like <<sql-functions-aggs-min,`MIN`>>, <<sql-functions-aggs-max,`MAX`>>, etc. can only be used
+directly on fields, and so queries like `SELECT MAX(abs(age)) FROM test` are not possible.
+
[float]
=== Using a sub-select
@@ -92,7 +98,7 @@ But, if the sub-select would include a `GROUP BY` or `HAVING` or the enclosing `
FROM (SELECT ...) WHERE [simple_condition]`, this is currently **un-supported**.
[float]
-=== Use <<sql-functions-aggs-first, `FIRST`>>/<<sql-functions-aggs-last,`LAST`>> aggregation functions in `HAVING` clause
+=== Using <<sql-functions-aggs-first,`FIRST`>>/<<sql-functions-aggs-last,`LAST`>> aggregation functions in `HAVING` clause
Using `FIRST` and `LAST` in the `HAVING` clause is not supported. The same applies to
<<sql-functions-aggs-min,`MIN`>> and <<sql-functions-aggs-max,`MAX`>> when their target column
