How long + past simple, present perfect or present perfect continuous.
How the meaning will be changed after using each of these tenses ?
I don't know if I got it right, so I want to share the way I understand it and to be corrected if got something wrong.
For example how the meaning will be different with this sentence: how long (work) for them.
How long did David work for them
would mean that David worked for them previously but doesn't work for them anymore.
How long has David worked for them
would mean that David works for them generally and I'm asking how long does he do it?
Present perfect continuous:
How long has David been working for them
would mean that David works for them at the time of speaking?
I have doubts about the Present perfect and the Present perfect continuous. I think didn't understand them correctly.