More explicit exception message for invalid key columns

engine/table/src/main/java/io/deephaven/engine/table/impl/by/ChunkedOperatorAggregationHelper.java

@@ -45,11 +45,9 @@
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.LinkedHashMap;
-import java.util.Map;
+import java.util.*;
 import java.util.function.LongFunction;
+import java.util.function.Predicate;
 import java.util.function.Supplier;
 import java.util.function.UnaryOperator;
 
@@ -90,19 +88,31 @@ public static QueryTable aggregation(
             @NotNull final Collection<? extends ColumnName> groupByColumns) {
         final String[] keyNames = groupByColumns.stream().map(ColumnName::name).toArray(String[]::new);
         if (!input.hasColumns(keyNames)) {
+            final Set<String> colNames = input.getColumnSourceMap().keySet();
+            final String[] missingColumns = Arrays.stream(keyNames)
+                    .filter(Predicate.not(colNames::contains))
+                    .toArray(String[]::new);;
+
             throw new IllegalArgumentException("aggregation: not all group-by columns " + Arrays.toString(keyNames)
                     + " are present in input table with columns "
-                    + Arrays.toString(input.getDefinition().getColumnNamesArray()));
+                    + Arrays.toString(input.getDefinition().getColumnNamesArray()) + ". Missing columns: "
+                    + Arrays.toString(missingColumns));
         }
         if (initialKeys != null) {
             if (keyNames.length == 0) {
                 throw new IllegalArgumentException(
                         "aggregation: initial groups must not be specified if no group-by columns are specified");
             }
             if (!initialKeys.hasColumns(keyNames)) {
+                final Set<String> colNames = input.getColumnSourceMap().keySet();
+                final String[] missingColumns = Arrays.stream(keyNames)
+                        .filter(Predicate.not(colNames::contains))
+                        .toArray(String[]::new);;
+
                 throw new IllegalArgumentException("aggregation: not all group-by columns " + Arrays.toString(keyNames)
                         + " are present in initial groups table with columns "
-                        + Arrays.toString(initialKeys.getDefinition().getColumnNamesArray()));
+                        + Arrays.toString(initialKeys.getDefinition().getColumnNamesArray()) + ". Missing columns: "
+                        + Arrays.toString(missingColumns));
             }
             for (final String keyName : keyNames) {
                 final ColumnDefinition<?> inputDef = input.getDefinition().getColumn(keyName);

engine/table/src/test/java/io/deephaven/engine/table/impl/QueryTableAggregationTest.java

@@ -74,7 +74,7 @@
 import static io.deephaven.engine.util.TableTools.*;
 import static io.deephaven.util.QueryConstants.*;
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.*;
 
 @Category(OutOfBandTest.class)
 public class QueryTableAggregationTest {
@@ -3834,6 +3834,22 @@ public void testPreserveEmptyNoKey() {
         assertTableEquals(expectedEmpty, aggregated);
     }
 
+    @Test
+    public void testKeyColumnMissing() {
+        final Table data = testTable(col("S", "A", "B", "C", "D"), col("I", 10, 20, 30, 40));
+        try {
+            final Table agg = data.selectDistinct("NonExistentCol");
+            fail("Should have thrown an exception");
+        } catch (Exception ex) {
+            io.deephaven.base.verify.Assert.instanceOf(ex, "ex", IllegalArgumentException.class);
+            io.deephaven.base.verify.Assert.assertion(
+                    ex.getMessage().contains("Missing columns: [NonExistentCol]"),
+                    "ex.getMessage().contains(\"Missing columns: [NonExistentCol]\")",
+                    ex.getMessage(),
+                    "ex.getMessage()");
+        }
+    }
+
     @Test
     public void testMultiPartitionSymbolTableBy() throws IOException {
         final File testRootFile = Files.createTempDirectory(QueryTableAggregationTest.class.getName()).toFile();