Insert into List(Text) Field
As for any application, unless you are perfectly sure of what you are doing, are comfortable with it and have a good understanding of the inner working of the Field API and the SQL storage engine for fields, you shouldn't try to do your insert directly in SQL.

Instead, you should use the Node or Entity APIs to load your contents, update them and save them back in PHP code. This will be more expensive performance-wise, but much more easier to implement and maintain.