fix count on distinctTimestamp

adds the ability to get the count of a distinct call to a timestamp field

executor.go

@@ -5027,6 +5027,8 @@ func (e *executor) executeCount(ctx context.Context, qcx *Qcx, index string, c *
 			return row.Count(), nil
 		case SignedRow:
 			return row.Pos.Count() + row.Neg.Count(), nil
+		case DistinctTimestamp:
+			return uint64(len(row.Values)), nil
 		default:
 			return 0, errors.Errorf("cannot count result of type %T from call %q", row, child.String())
 		}

executor_test.go

@@ -6756,6 +6756,29 @@ func TestExecutor_Execute_CountDistinct(t *testing.T) {
 	})
 }
 
+func TestExecutor_Execute_CountDistinctTimestamp(t *testing.T) {
+	index := "test_index"
+	field := "ts"
+	c := test.MustRunCluster(t, 1)
+	defer c.Close()
+
+	// create an index and timestamp field
+	c.CreateField(t, index, pilosa.IndexOptions{}, field, pilosa.OptFieldTypeTimestamp(time.Unix(0, 0), "s"))
+
+	// add some data
+	data := []string{"2010-01-02T12:32:00Z", "2010-04-20T12:32:00Z", "2011-04-20T12:32:00Z"}
+	for i, datum := range data {
+		c.Query(t, index, fmt.Sprintf("Set(%d, ts=\"%s\")", i+10, datum))
+	}
+
+	// query the Count of Distinct vals in field ts
+	count := c.Query(t, index, "Count(Distinct(field=ts))").Results[0]
+	if count != len(data) {
+		t.Fatalf("expected %v got %v", len(data), count)
+	}
+
+}
+
 // Ensure that a top-level, bare distinct on multiple nodes
 // is handled correctly.
 func TestExecutor_BareDistinct(t *testing.T) {