CREATE TABLE table_27374004_4 (date_of_vacancy VARCHAR2, outgoing_manager VARCHAR2)

How many times did outgoing manager Bart de Roover vacated a position?
SELECT COUNT(date_of_vacancy) FROM table_27374004_4 WHERE outgoing_manager = "Bart De Roover"
SELECT COUNT("date_of_vacancy") FROM "table_27374004_4" WHERE "Bart De Roover" = "outgoing_manager"