here is the table for question

id mgrid depno

1 null 10
2 null 20
3 1 20
4 2 10
5 3 10

explation: in above table id - "1" has depno 10 and id - "3" has depno 20 but "1" is manager of "3". so id - "3" should have depno 10.
similarly id - "4" should have depno 20.
similarly we need to check this for id - "5".

i want to do this with single update query. please let me know what should be query for this?

i need to update this table and correct the wrong entries for id 3 and 4.
should fill depno = 10 for id 3 and depno = 20 for id 4.
query should also check it for id 5 as its value already correct.

I think your issue is to prevent the wrong depno's in the database in the first place.

Otherwise, I don't see any usable logic to determine which rows need to get updated.

Something like:

UPDATE [Table] SET depno = 20 WHERE id IN (SELECT id FROM [Table Employee] WHERE [Column 1] IN (id's that need to be updated to 20))

Post the logic and please look at why the wrong depno is getting saved to the table in the first place.