Deterministic use of DuckDB "last" function (#5291)

runtime/queries/column_timeseries.go

@@ -649,7 +649,14 @@ func getCoalesceStatementsMeasures(measures []*runtimev1.ColumnTimeSeriesRequest
 func getCoalesceStatementsMeasuresLast(dialect drivers.Dialect, measures []*runtimev1.ColumnTimeSeriesRequest_BasicMeasure) string {
 	var result string
 	for i, measure := range measures {
-		result += fmt.Sprintf(` `+lastValue(dialect)+`(%[1]s) as %[1]s`, safeName(measure.SqlName))
+		switch dialect {
+		case drivers.DialectDuckDB:
+			// "last" function of DuckDB returns non-deterministic results by default so requires an ORDER BY clause
+			// https://duckdb.org/docs/sql/functions/aggregates.html#order-by-clause-in-aggregate-functions
+			result += fmt.Sprintf(` `+lastValue(dialect)+`(%[1]s ORDER BY %[1]s NULLS FIRST) as %[1]s`, safeName(measure.SqlName))
+		default:
+			result += fmt.Sprintf(` `+lastValue(dialect)+`(%[1]s) as %[1]s`, safeName(measure.SqlName))
+		}
 		if i < len(measures)-1 {
 			result += ", "
 		}