Merge pull request #8746 from planetscale/fix-8694-in-11

Backport to 11: Fixing a panic in vtgate with OLAP mode

go/test/endtoend/vtgate/misc_test.go

@@ -704,6 +704,26 @@ ts12 TIMESTAMP DEFAULT LOCALTIME()
 	exec(t, conn, "drop table function_default")
 }
 
+func TestRenameFieldsOnOLAP(t *testing.T) {
+	defer cluster.PanicHandler(t)
+	ctx := context.Background()
+	conn, err := mysql.Connect(ctx, &vtParams)
+	require.NoError(t, err)
+	defer conn.Close()
+
+	_ = exec(t, conn, "set workload = olap")
+	defer func() {
+		exec(t, conn, "set workload = oltp")
+	}()
+
+	qr := exec(t, conn, "show tables")
+	require.Equal(t, 1, len(qr.Fields))
+	assert.Equal(t, `Tables_in_ks`, fmt.Sprintf("%v", qr.Fields[0].Name))
+	_ = exec(t, conn, "use mysql")
+	qr = exec(t, conn, "select @@workload")
+	assert.Equal(t, `[[VARBINARY("OLAP")]]`, fmt.Sprintf("%v", qr.Rows))
+}
+
 func assertMatches(t *testing.T, conn *mysql.Conn, query, expected string) {
 	t.Helper()
 	qr := exec(t, conn, query)

go/vt/vtgate/engine/rename_fields.go

@@ -74,6 +74,9 @@ func (r *RenameFields) Execute(vcursor VCursor, bindVars map[string]*querypb.Bin
 
 func (r *RenameFields) renameFields(qr *sqltypes.Result) {
 	for ind, index := range r.Indices {
+		if index >= len(qr.Fields) {
+			continue
+		}
 		colName := r.Cols[ind]
 		qr.Fields[index].Name = colName
 	}
@@ -84,7 +87,11 @@ func (r *RenameFields) StreamExecute(vcursor VCursor, bindVars map[string]*query
 	if wantfields {
 		innerCallback := callback
 		callback = func(result *sqltypes.Result) error {
-			r.renameFields(result)
+			// Only the first callback will contain the fields.
+			// This check is to avoid going over the RenameFields indices when no fields are present in the result set.
+			if len(result.Fields) != 0 {
+				r.renameFields(result)
+			}
 			return innerCallback(result)
 		}
 	}