Git usually guesses correctly whether a blob contains text or binary data by examining the beginning of the contents. In your case, however, git is getting confused and treating the file as binary, possibly due to binary data somewhere in the file.
From the git-diff manpage:
-a, --text
Treat all files as text.
So you can still get the text diff quite easily as follows:
git diff -a WebRole/Sql/Objects/dbo.Content.Table.sql
To override git incorrect guess add the following to .gitattributes in the same directory as the file:
*.sql diff
and commit this file. This will force git to treat every .sql file as text from now on, wether or not it contains binary data.