Help getting SQL Error Codes?

[danthegoodman1]

For example, if I try to insert a row in which the primary key already exists (postgres/CRDB), I would like to be able to look at the corresponding code 23505 to determine how the handle the error.

I'm struggling to find out how to extract these error codes from the error returned.

[aarondl]

errors.As should work with this library for introspecting errors that are returned.