docs: DOC-1091: Rollup topic should mention that only Strings and primitives are allowed types for rollup by (#7542)

https://deephaven.atlassian.net/browse/DOC-1091

Author: elijahpetty

docs/groovy/assets/how-to/cant-parse-local-date.png

@@ -113,6 +113,33 @@ result = source.rollup(aggList, "Group", "Subgroup")
 
 ![Creating a rollup table](../assets/how-to/new-rollup.gif)
 
+Note that rollup tables can only be created from String or primitive columns. Attempting to use a non-primitive type such as `LocalDate` or a Timestamp as a rollup column results in an error:
+
+```groovy skip-test
+import io.deephaven.api.agg.Aggregation
+
+t = newTable(
+    stringCol("Sym", "AAPL", "AAPL", "GOOGL", "GOOGL", "AAPL"),
+    doubleCol("Last", 150.25, 151.50, 920.75, 922.10, 152.00),
+    intCol("Size", 100, 200, 50, 150, 300),
+    instantCol("ExchangeTimestamp",
+        parseInstant("2017-08-25T09:30:00 UTC"),
+        parseInstant("2017-08-25T10:15:00 UTC"),
+        parseInstant("2017-08-25T11:45:00 UTC"),
+        parseInstant("2017-08-25T14:20:00 UTC"),
+        parseInstant("2017-08-25T15:50:00 UTC")
+    )
+)
+
+t = t.update("LocalExchangeTimestampDate=toLocalDate(ExchangeTimestamp, timeZone(`UTC`))")
+
+aggList = [Aggregation.AggAvg("Last", "Size")]
+
+tRollup = t.rollup(aggList, "LocalExchangeTimestampDate")
+```
+
+![An error message stating that Deephaven can't parse the LOCAL_DATE data type](../assets/how-to/cant-parse-local-date.png)
+
 ## Related documentation
 
 - [How to create a hierarchical tree table](./tree-table.md)

docs/groovy/how-to-guides/rollup-table.md

@@ -117,6 +117,43 @@ result = source.rollup(aggs=agg_list, by=by_list)
 
 ![Creating a rollup table](../assets/how-to/new-rollup.gif)
 
+Note that rollup tables can only be created from String or primitive columns. Attempting to use a non-primitive type such as `LocalDate` or a Timestamp as a rollup column results in an error:
+
+```python skip-test
+from deephaven import new_table, agg
+from deephaven.column import string_col, int_col, double_col, datetime_col
+from deephaven.time import to_j_instant
+
+t = new_table(
+    [
+        datetime_col(
+            "ExchangeTimestamp",
+            [
+                to_j_instant("2017-08-25T09:30:00 UTC"),
+                to_j_instant("2017-08-25T10:15:00 UTC"),
+                to_j_instant("2017-08-25T11:45:00 UTC"),
+                to_j_instant("2017-08-25T14:20:00 UTC"),
+                to_j_instant("2017-08-25T15:50:00 UTC"),
+            ],
+        ),
+        string_col("Sym", ["AAPL", "AAPL", "GOOGL", "GOOGL", "AAPL"]),
+        double_col("Last", [150.25, 151.50, 920.75, 922.10, 152.00]),
+        int_col("Size", [100, 200, 50, 150, 300]),
+    ]
+)
+
+t = t.update(
+    "LocalExchangeTimestampDate=toLocalDate(ExchangeTimestamp, timeZone(`UTC`))"
+)
+
+agg_list = [agg.avg(cols=["Last", "Size"])]
+by_list = ["LocalExchangeTimestampDate"]
+
+t_rollup = t.rollup(aggs=agg_list, by=by_list, include_constituents=True)
+```
+
+![An error message stating that Deephaven can't parse the LOCAL_DATE data type](../assets/how-to/cant-parse-local-date.png)
+
 ## Related documentation
 
 - [How to create a hierarchical tree table](./tree-table.md)