SQL多条件查询

表A有列 F1,F2,F3 ; 我理解的意思是组合查询, 按照3个列的条件: select * from A where (f1 = '参数1' or '参数1' is null) and (f2 = '参数2' or '参数2' is null) and (f3 = '参数3' or '参数3' is null)