2 Posts Tagged ‘sql’

(All tags.)

How to Check Multiple Tables Are Empty in SQL

Look Out! Empty Tables Ahoy!

I encountered this problem recently for a Django ticket for speeding up part of Django’s test runner. We have a list of tables to truncate. How can we figure out which are already empty, so we can skip issuing a somewhat costly TRUNCATE TABLE on them? You might think the database could skip TRUNCATE TABLE on empty tables, but it normally does work beyond removing the rows such as resetting auto-increment counters. In MySQL, TRUNCATE TABLE is even equivalent to DROP TABLE and CREATE TABLE, which requires removing and creating the table file on disk.


SQL’s Implicit Type Conversion

Birds of a feather convert together

At yesterday’s DJUGL meetup I heard a talk from Esau Rodríguez about a buggy new system deployment he survived. His team were deploying a new version of a system that changed the way it connected to its MySQL database, while simultaneously moving session keys from integers to UUID’s. When they discovered the database connection change was flaky, they rolled back to the previous version. This quickly lead to a user reporting being able to see another’s data!