be another matter/thing

​

to be a different situation that is likely to be judged differently

另当别论;情况不同

Cars are useful, but their impact on the environment is another matter altogether.

汽车很有用，但对环境的影响则应另当别论。

She didn’t mind seeing him in a group but an intimate dinner in a restaurant was another matter altogether.

跟大家在一起时见见他，她并不介意，但是在饭店里亲密进餐就另当别论了。