sql中筛选条件为空值

 process_instance_id is null or ifnull(process_instance_id,'')=''

select * from blade_process_should_pay_invoice
where is_deleted = 0
and process_instance_id is null or ifnull(process_instance_id,'')=''
and create_user = '1273086723649093633'
order by create_time desc