I don’t often have fields much longer than 256 char, but a web application I am working on makes use of varchar 512. I’m not really able to change the field to text as the PHP Docs suggest. MS SQL doesn’t allow the equal operator, and grouping on text fields, and it’s also very slow compared to a varchar which can make advanced queries very difficult. “Due to a limitation in the underlying API used by PHP (MS DBLib C API), the length of VARCHAR fields is limited to 255″
Basically, it appears that PHP is using some old C API from Microsoft and to get around this need to convert from varchar to text. Text by default, allows about 8,000 characters but changing this fairly simple in the php.ini
mssql.textlimit = 65536
mssql.textsize = 65536
Of course, you can also set it dynamically using ini_set.
ini_set("mssql.textlimit", '65536' );
ini_set("mssql.textsize", '65536' );
Hope this helps.