The update query is ill-formed. There are no conditions joining tables `times` and `pathway` expressed in the query. It devolves to simply: update times set block_id = 6 where block_id == 3; with a useless reference to table `pathway`. While this should not be harmful (other than doing a table scan to cross join `times` and `pathway` for each candidate where `times.block_id == 3`) it should not cause a problem. However, depending on how many rows are in the tables, the cross join operation could take a very long time.