user: Question: How many characters were portrayed by the Informant of Don Flack?
Columns: ['Character', 'Portrayed by', 'Relationship', 'First appearance', 'Last appearance']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Reed Garrett', 'Kyle Gallner', "Son of Mac Taylor's late wife", '"Consequences"', '"Pot of Gold"']
SQL:

assistant: SELECT COUNT("Portrayed by") FROM "Table" WHERE "Relationship" = 'Informant of Don Flack';