Pfthb

Right now if there is an error, such as duplicate entry, I return it like this res.status(500).send(err);

Showing the client this kind of things:

 "code": "ER_DUP_ENTRY",
 "errno": 1062,
 "sqlMessage": "Duplicate entry 'name@mail.com' for key 'user_table_email_unique'",
 "sqlState": "23000",
 "index": 0,
 "sql": "update `user_table` set `email` = 'name@mail.com' where `id` = 3"

What is the standard way of doing this? I want the client to know what kind of error is but not, for example, the name of my tables

without seeing your code structure it's difficult to help, but if you have your query in a function that returns to your main script you could catch there, process the error and then throw a succinct and non-data exposing error back to the calling function.

// This is pseudocode
const updateEmail = (db, email, id) => db.query('query...')
 .then(data => /* process things */)
 .catch(err => 
 if (err.errno === 1062) 
 throw new Error('Email already exists');
 
 );

I'm not certain that 500 is the correct code to use in this particular case either, as it isn't a server error per se. That would be a preference thing though depending upon how your other requests are structured.