Query failed

I’m attempting to use this plugin to use an external database as an identity authenticator – but I can’t get past the “test connection” The only thing that appears when I test is the statement “Query failed”?

I’m not sure I have the Table Mapping set up correctly: when specifying the fielsd names, do I include the table name as well, e.g., “users.username” or just “username”

Also, my salt is in the same field as the password hash – what do I put in the salt field name? same as password?

Finally, do I have to specify the email, first and last name – the external database does not have those fields – just username and password.

I’ve tried every combination I can think of and all I get is “Query failed”

Help!