Question

Hi all I’ve got an interesting task to update a single column in a table that has roughly 2 million rows. I’ve tried doing this using MVC Entity Framework, however I’m encountering “Out of memory exceptions” and I’m just wondering if there’s another way.

The interesting part is that its not just a simple update. The procedure needs to read the TelephoneNumber column already in the table and this could be 014812001 for example. Then it needs to calculate a score for this number based on the number of occurrences greater than 1. So for example using the above number this would score a 6 as we have 3 x 1’s and 3 x 0’s giving a total of 6.

Once this score has been calculated this number needs to be inserted into the a column in the current row be processed, so in our case the row with the TelephoneNumber = 014812001.

Is this possible using TSQL or is it better to carry on with my Entity Framework approach?

Answer 1

For such a bulk update, I would always recommend doing this on the server itself – there’s really no point in dragging down 2 million rows, updating a single column, and then pushing those back to the server again…..

I think based on your description, it should be fairly simple to create a little T-SQL user defined function that would calculate this score. Once you have that, you can issue a single T-SQL statement:

UPDATE dbo.YourTable
SET Score = dbo.fnCalculateScore(TelephoneNumber)
WHERE .... (whatever condition you might have) .....

That should be faster by several orders of magnitude than with your Entity Framework approach….