I noticed some weird update behaviour today in one of our development environments. In my opinion this appears to be a bug, but before reporting it I thought I should seek the opinions of others in the community. Maybe this is known and/or seen before?
The behaviour is visible when a subquery is used in an update. More specifically when a subquery is rejected by the parser when executed on it's own. This causes the where condition to be ignored entirely and thus the whole table updated rather than the parser throwing an error.