diff --git a/read_buffer/src/chunk.rs b/read_buffer/src/chunk.rs
index 506b0d3338..e02d999e42 100644
--- a/read_buffer/src/chunk.rs
+++ b/read_buffer/src/chunk.rs
@@ -4,7 +4,7 @@ use std::{
 };
 
 use internal_types::selection::Selection;
-use snafu::{ResultExt, Snafu};
+use snafu::{OptionExt, ResultExt, Snafu};
 
 use crate::row_group::RowGroup;
 use crate::row_group::{ColumnName, Predicate};
@@ -184,9 +184,7 @@ impl Chunk {
         let table = chunk_data
             .data
             .get(table_name)
-            .ok_or(Error::TableNotFound {
-                table_name: table_name.to_owned(),
-            })?;
+            .context(TableNotFound { table_name })?;
 
         Ok(table.read_filter(select_columns, predicate))
     }
@@ -195,7 +193,7 @@ impl Chunk {
     /// columns, optionally filtered by the provided predicate. Results are
     /// merged across all row groups within the returned table.
     ///
-    /// Returns `None` if the table no longer exists within the chunk.
+    /// Returns an error if the specified table does not exist.
     ///
     /// Note: `read_aggregate` currently only supports grouping on "tag"
     /// columns.
@@ -205,17 +203,18 @@ impl Chunk {
         predicate: Predicate,
         group_columns: &Selection<'_>,
         aggregates: &[(ColumnName<'_>, AggregateType)],
-    ) -> Option<table::ReadAggregateResults> {
+    ) -> Result<table::ReadAggregateResults> {
         // read lock on chunk.
         let chunk_data = self.chunk_data.read().unwrap();
 
-        // Lookup table by name and dispatch execution.
-        //
-        // TODO(edd): this should return an error
-        chunk_data
+        let table = chunk_data
             .data
             .get(table_name)
-            .map(|table| table.read_aggregate(predicate, group_columns, aggregates))
+            .context(TableNotFound { table_name })?;
+
+        table
+            .read_aggregate(predicate, group_columns, aggregates)
+            .context(TableError)
     }
 
     //
diff --git a/read_buffer/src/lib.rs b/read_buffer/src/lib.rs
index af21e2d92a..23d2372ee6 100644
--- a/read_buffer/src/lib.rs
+++ b/read_buffer/src/lib.rs
@@ -363,11 +363,11 @@ impl Database {
             // Get all relevant row groups for this chunk's table. This
             // is cheap because it doesn't execute the read operation,
             // but just gets references to the needed to data to do so.
-            if let Some(table_results) =
-                chunk.read_aggregate(table_name, predicate.clone(), &group_columns, &aggregates)
-            {
-                chunk_table_results.push(table_results);
-            }
+            let table_results = chunk
+                .read_aggregate(table_name, predicate.clone(), &group_columns, &aggregates)
+                .context(ChunkError)?;
+
+            chunk_table_results.push(table_results);
         }
 
         Ok(ReadAggregateResults::new(chunk_table_results))
diff --git a/read_buffer/src/table.rs b/read_buffer/src/table.rs
index 3ebf687e80..7e68a13857 100644
--- a/read_buffer/src/table.rs
+++ b/read_buffer/src/table.rs
@@ -228,7 +228,7 @@ impl Table {
         predicate: Predicate,
         group_columns: &'input Selection<'_>,
         aggregates: &'input [(ColumnName<'input>, AggregateType)],
-    ) -> ReadAggregateResults {
+    ) -> Result<ReadAggregateResults> {
         let (meta, row_groups) = self.filter_row_groups(&predicate);
 
         // Filter out any column names that we do not have data for.
@@ -241,13 +241,24 @@ impl Table {
             ..ResultSchema::default()
         };
 
+        // Check all grouping columns are valid for grouping operation.
+        for (ct, _) in &schema.group_columns {
+            ensure!(
+                matches!(ct, ColumnType::Tag(_)),
+                UnsupportedColumnOperation {
+                    msg: format!("column type must be ColumnType::Tag, got {:?}", ct),
+                    column_name: ct.as_str().to_string(),
+                },
+            )
+        }
+
         // return the iterator to build the results.
-        ReadAggregateResults {
+        Ok(ReadAggregateResults {
             schema,
             predicate,
             row_groups,
             ..Default::default()
-        }
+        })
     }
 
     /// Returns aggregates segmented by grouping keys and windowed by time.
@@ -1064,11 +1075,13 @@ mod test {
         table.add_row_group(rg);
 
         // no predicate aggregate
-        let mut results = table.read_aggregate(
-            Predicate::default(),
-            &Selection::Some(&[]),
-            &[("time", AggregateType::Count), ("time", AggregateType::Sum)],
-        );
+        let mut results = table
+            .read_aggregate(
+                Predicate::default(),
+                &Selection::Some(&[]),
+                &[("time", AggregateType::Count), ("time", AggregateType::Sum)],
+            )
+            .unwrap();
 
         // check the column result schema
         let exp_schema = ResultSchema {
@@ -1095,17 +1108,31 @@ mod test {
         assert!(matches!(results.next_merged_result(), None));
 
         // apply a predicate
-        let mut results = table.read_aggregate(
-            Predicate::new(vec![BinaryExpr::from(("region", "=", "west"))]),
-            &Selection::Some(&[]),
-            &[("time", AggregateType::Count), ("time", AggregateType::Sum)],
-        );
+        let mut results = table
+            .read_aggregate(
+                Predicate::new(vec![BinaryExpr::from(("region", "=", "west"))]),
+                &Selection::Some(&[]),
+                &[("time", AggregateType::Count), ("time", AggregateType::Sum)],
+            )
+            .unwrap();
 
         assert_eq!(
             DisplayReadAggregateResults(vec![results.next_merged_result().unwrap()]).to_string(),
             "time_count,time_sum\n2,300\n",
         );
         assert!(matches!(results.next_merged_result(), None));
+
+        // group on wrong columns.
+        let results = table.read_aggregate(
+            Predicate::new(vec![BinaryExpr::from(("region", "=", "west"))]),
+            &Selection::Some(&["time"]),
+            &[("min", AggregateType::Min)],
+        );
+
+        assert!(matches!(
+            &results,
+            Err(Error::UnsupportedColumnOperation { .. })
+        ),);
     }
 
     #[test]