I'm trying to create a select to update a record, but I get an error when executing this
does anyone know how to solve?
You have a couple problems with this query which will apply to all database, not just Postgres. Both of these problems stem from the fact that Retool uses parameterized queries, so it follows the basic rules of this (Google it for more info)
First off, you do not need the quotes around the values. This will be done for you by the parameterization process if the field needs it.
Related: databases need single quotes, not double quotes to speficy string values. Double quotes are reserved for field names, not field values. That doesn't make a difference here as you need none, but thought you should know.
Second, the syntax for your email value is wrong. You need something like this to make the parameterization happy:
{{username.value + '@gmail.com'}}
That should get you up and running.