consider this as my table where i have an requirement
where i need to truncate just the column cash_in_hand
but if i do something like this
then it will delete the entire row with credit & debit information
but i need to delete only cash_in_hand column how to do that ?

note : i need to delete only data not the structure of cash_in_hand

update table set cash_in_hand = NULL ???

SQL Server (and all the RDBMSs too) stores data on a row-basis. This means that your requirement does not have any sense. You can put the column data to NULL as already suggested, but this is just a data approach.
Unless your requirement is about storage space.

can you explain what you want to happen in terms of the real world as opposed to the database? What you are describing resembles "I want to paint that rain cloud red." which may be possible under some circumstances, but doesn't make much sense and seems like it would require far more effort than it might justify.

If we could understand what you're trying to accomplish, we can probably offer you a good answer. Based on your description of your problem so far, baburajv has offered the best answer I can imagine.

-PatP

A variable value like cash in hand ought not to be stored in a table. Create a view to show this as the difference between the credit and debit values, and that way you will always have the current value available.

weejas, that can be a very expensive query to run time after time. I'm all for dynamically calculating when possible, but performing the same expensive calculations time after time on historical data, always getting the exact same result, begs for storing the data in the row.

This is true. However, it depends on how many transactions there are and how many times the information is required on a daily basis as to whether the performance hit will be a deal-breaker. For example, I work with two ERPSs, and neither of them store the stock on hand in the inventory.

Also, whether you're running a query over the whole table to sum transactions for display or running a query over the whole table to sum transactions for storage, you're still running the query over the same table.

Do I need to point out that you run it only once for storage, and it can be performed during off-hours?

And do I need to point out that if you run such a query overnight, your balances will not reflect any transactions since then? :P

There are pros and cons to both approaches. I favour calculating such totals as and when they are required, but I accept that it is possible to store them too, and in some cases is preferable.

Apparently I need to point out that it need be run across the table only once, for existing data.
A trigger or procedure code can keep individual records updated, very efficiently.
Apparently, that needed to be pointed out.

ding...ding...ding...ding....we have a winner

Johnny, tell'em what he's won

Dong...dong...dong...dong...dong!
That answered his question, but did not solve his problem.

Where did Oppie say that?

Brett, read the post history.
The problem is how best to handle a calculated value such as cash in hand.
The discussion was whether CashInHand should be stored in the table at all.
This is clearly pertinent to both the original poster, and others who encounter this thread with similar problems.