Update query-engine.md

Author: soispoke

docs/reference/dune-v2/query-engine.md

@@ -43,6 +43,8 @@ The syntax and keyword operator differences between Postgres, Spark, and Dune SQ
 | **String Data Type** | `varchar` | `string` | `varchar` |
 | **Casting as Strings** | `cast([xxx] as string)` | `cast([xxx] as string)` | `cast([xxx] as varchar)` |
 | **`left()` is no longer a method available for returning substrings** | `left([string],[length])` | `left([string],[length])` | `substr([string], [start], [length])` <br><br> [Returns varchar; Positions start with 1, so use `1` for length if you want to replicate left() functionality](https://trino.io/docs/current/functions/string.html?highlight=substr#substring)|
+| **Aggregate Functions** | `array_agg(col)`, `array_agg(distinct(col))` | `array_agg(col)` or `collect_list(col)`, `collect_set(col)` or `array_agg(distinct(col))` | `array_agg(col)`, `array_agg(distinct(col))` |
+
 
 left(somestring, somenumber) -> substr(somestring, 0, somenumber)