Using varchar(max) columns within views as comparison keys.

dfash

I have a view where the two columns I want to use as comparison keys are defined as varchar(max). When I go to select the key fields I am unable to select either of these columns. Is there an option somewhere to allow this? I am running v8.0.2.5.

Chris Auckland

Thanks for your post.

BLOBS's and (max) data types are not supported as comprison keys in SQL Data Compare. I imagine this is due to performance reasons, as there could potentially be very large amounts of data in the column.

Also, as I understand it, when a MAX data type exceeds a certain size, an overflow page is used. I'm not sure what implications this would have on a comparison key in SQL Data Compare.

I'll see if I can find out exactly why these data types are unsupported and let you know.

Chris Auckland

It seems that there is a bug in the native data reader that causes BLOBS and (MAX) data types to be read in their entirety, causing SQL Data Compare to run out of memory and fall over.

We attempted to write our own data reader to get round this problem, but this seemed to introduce more problems than it solved, so we returned to using the native reader.

For this reason BLOB's and (MAX) data types are not supported for comparison keys in the current version.

Hopefully it is something that can be addressed in a future version, but currently it isn't possible.