Actually I can add a default value in the admin page under Configu => Subscribe pages => Edit
add the following line to my config.php file:
define( 'EMPTY_VALUE_PREFIX' , '--' ) ;
Either method I still need to add a record to my database table
listattr_... and the record's
name has to match my default value. Thank you @duncanc for this reminder.
That solves my initial question but leads me to another question / dilemma...
The select attribute I am offering is a list of countries. I am using the ISO 3166-1 country code list and importing it into my table
listattr_country, with the ISO-3166-1 numeric code as the record
id. So when I go and add a record for the default value, I am giving it a record
id of 0. I need this record
id to be 0 so that I can query if a valid country was selected. Since the column
id is the primary key, any DBA will tell you it is bad to have the
id of 0. MySQL will complain if I do a table integrity check. I guess I could give it some ridiculously high record
id so ISO-3166 would never reach in the future. Or, I could modify the phpList code so that default value is not inserted into the database... but then I won't be compatible with future upgrades.