Oracle使用to_date()格式化日期会遇到什么坑

select * from daily_file_information;

select to_char(dfi_create_time,'yyyy-mm'),count(1) from daily_file_information  group by to_char(dfi_create_time,'yyyy-mm');

select count(1) from daily_file_information where 1=1 and to_char(dfi_create_time,'yyyy-mm') between '2020-03' and '2020-05' ;

select count(1) from daily_file_information where 1=1 and dfi_create_time between to_date('2020-03','yyyy-mm') and to_date('2020-05','yyyy-mm')  ;

select count(1) from daily_file_information where 1=1 and to_char(dfi_create_time,'yyyy-mm') >= '2020-03' and to_char(dfi_create_time,'yyyy-mm') <= '2020-05' ;

select count(1) from daily_file_information where 1=1 and dfi_create_time >= to_date('2020-03','yyyy-mm') and dfi_create_time <= to_date('2020-05','yyyy-mm')  ;