So if they enter 1,000 instead of 1000 and don’t get an error then how are they to know that they need to remove the comma?
It all depends on the reason for the error. If the error is the user’s fault then they should get an error message. If it is a system fault then it should be logged. Either way storing them in the database should be fine - particularly since the info the user is entering needs to be processed against the database anyway so if the DB is down then their input will not work even if they don’t make an error.
Yes, there is a big difference between
“Sorry, system problems, please try again in a few minutes”
“Error in ‘/database/connect.php’ line 12, Unable to write to member_emails field in member_data table”
If the database is puking, it should have an error reported in a log and usually the admin should get some sort of notification (an email as a minimum). The user should get a “Sorry, we are out of order.” page. Storing the text for any other error messages in the database or a central file or caching system is a normal practice, especially for scaling apps.