add note about MySQL and MariaDB re: offset (#45219)

docs/questions/query-builder/expressions-list.md

@@ -728,6 +728,8 @@ Example: `year("2021-03-25T12:52:37")` would return the year 2021 as an integer,
 
 ### Offset
 
+> The `Offset` function is currently unavailable for MySQL/MariaDB.
+
 Returns the value of an expression in a different row. `Offset` can only be used in the query builder's Summarize step (you cannot use `Offset` to create a custom column).
 
 Syntax: `Offset(expression, rowOffset)`

docs/questions/query-builder/expressions/offset.md

@@ -4,6 +4,8 @@ title: Offset
 
 # Offset
 
+> The `Offset` function is currently unavailable for MySQL/MariaDB.
+
 The `Offset` function returns the value of an expression in a different row. `Offset` can only be used in the query builder's Summarize step (you cannot use `Offset` to create a custom column).
 
 Syntax: `Offset(expression, rowOffset)`