I've just been updated to 2023.2 and an SQL query which ran fine before now takes so long to run it times out. I tweaked it to work on a narrower date range, and it works so it looks like it's a performance thing rather than something breaking in the code. Has anyone else seen a SuiteQL performance change post upgrade?

Open a support ticket. They do fix regressions like this.

Fixed now; NS added some indexes to the db.