As you may know on SQL Server a varchar column can hold up to 8000 characters (each row can hold up to 8K, so it depends on the size of other columns), when you need to store more it is common to use the
ntextdatatypes. The problem with the
textdatatype however is that you can't call most string functions on the column, they also require more IO due to how they are stored internally.
In SQL Server 2005 Microsoft added support for
nvarchar(max), this new datatype can be used anywhere a regular length limited varchar can, but lets you store up to 2GB of data. Behind the scenes the
varchar(max)stores up to the as much of the text as it can in the row (up to 8K), and then creates additional pages for any additional text. So in a lot of cases the text content will fit in the row, requiring much less disk IO.
Microsoft is said to be deprecating the
ntextin future releases.
I also found an interesting blog entry which finds that when you alter a column from ntext/text to nvarchar(max)/varchar(max) the text content will still be stored in the external page, you should run
UPDATE tableName SET columnName=columnNamewhich will cause SQL server to store text more efficiently.