user: Question: How many times did outgoing manager Bart De Roover vacated a position?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment', 'Position in table']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Eupen', 'Danny Ost', 'Resigned', '4 September 2010', 'Ezio Capuano', '7 September 2010', '16th']
SQL:

assistant: SELECT COUNT("Date of vacancy") FROM "Table" WHERE "Outgoing manager" = 'Bart De Roover';