I am not familiar with MS SQL Server, however in Databases, they all have different types of data a field can hold. Such as in MYSQL, you have a TINY TEXT data type and a TEXT data type.
A TINY TEXT Datatype can only hold 255 characters.
A TEXT Datatype can hold 65,535 Characters.
It is all in how you set up your columns when you create that particular table. Now you said that you had it in a Text File located within your database- I would not think that a datatype assigned to a column would affect that though. SO, that leads us back to the question of the limitation of PHP, I just looked it up in the manual and I see no limitations, maybe I missed it though.