Database VIEW does not reflect the data in the underying TABLE

Question

Input:

The customer claims that the application (.NET) when querying for some data returns data different from when the customer looks into the data table directly

Answer 1

Yes, sort of.

Possible Causes:

1. The View needs to be refreshed or recompiled. Happens when source column definitions change and the View (or something it depends on) is using "*", can be nasty. Call sp_RefreshView. Can also happen because of views or functions (data sources) that it calls as well.

2. The View is looking at something different from what they/you think. They are looking at the wrong table or view.

3. The View is transforming the data in an unexpected way. It works right, just not like they expected.

4. The View is returning a different subset of the data than expected. Again, it works right, just not like they think.

5. They are looking at the wrong database/server or with a Logon/user identity that causes the View to alter what it shows. Particularly nefarious because unlike Management Studio, most client programs do not tell you what database/server they are pointed at.

Answer 2

it is possible if the underlying table has been changed and sp_refreshview has not been ran against the view, so the view will have missing columns if those were added to the table.

To see what I mean read how to make sure that the view will have the underlying table changes by using sp_refreshview

Answer 3

Assuming the view does not actually transform the data, technically it is possible if a corruption occurs. View retrieves data from one index, 'table' retrieves from another (ie. from clustered) and the two are out of sync. A DBCC CHECKDB should reveal the problem.

But human error is much more likely, ie. they are looking at different table than the view, or at different records.

Answer 4

For sure there are other things:

1) Derived attributes are pulling from wrong tables in the view
2) The view is using incorrect tables
3) incorrect or missing joins in the view

to name a few

Answer 5

You can create views with locking hints which would mean you might be getting a dirty read. Or alternatively when they access the table directly, they might be using locking hints which could be giving them a dirty read at that point.

Another possibility that users don't seem to understand is that the data is fluid. The data you read at 3:00 in a view may not be the same data that you see at 3:30 looking directly at the table becasue there have been changes in the meantime.

Answer 6

A few possibilities:

• Your .NET application may not be pointing to where you or they think it is pointing. For example, it's pointed to a test server by mistake

• If the view has an index on a float or numeric value, the value may appear different from the underlying query due to rounding

• The ANSI_NULLS setting is specific to the view when it was created. If it's different from the setting during the select(s) on the underlying tables it could cause discrepancies for certain kinds of queries

• The underlying table structures have changed and the view hasn't been refreshed (especially a problem if it uses "SELECT *")

I'll edit this post if I think of any others.

EDIT: Here's an example of how the ANSI_NULLS setting can throw off your results:

SET ANSI_NULLS ON

DECLARE
     @i     INT,
     @j     INT

SET @i = NULL
SET @j = 1

SELECT
     CASE WHEN @i <> @j THEN 'Not Equal' ELSE 'Equal' END

SET ANSI_NULLS OFF

SELECT
     CASE WHEN @i <> @j THEN 'Not Equal' ELSE 'Equal' END

The results which you should receive are:

Equal

Not Equal