只需告诉它插入一个空值即可:
INSERT Leads VALUES('name', 'cityName', 5, 'anotherValue')
INSERT Leads VALUES('name', 'cityName', null , 'anotherValue')
INSERT Leads VALUES('name', 'cityName', 2, 'anotherValue')
INSERT Leads VALUES('name', 'cityName', 9, 'anotherValue')