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.
Past simple:
How long did David work for them
would mean that David worked for them previously but doesn't work for them anymore.
Present perfect:
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.