fix

rowers/dataprep.py

@@ -2531,6 +2531,8 @@ def read_cols_df_sql(ids, columns, convertnewtons=True):
     columns = list(set(columns))
     ids = [int(id) for id in ids]
 
+    df = pd.DataFrame({})
+
 
     if len(ids) == 0:
         return pd.DataFrame(),extracols