Updating variable-length character data, or text or unitext columns, with the empty string ("") inserts a single space. Fixed-length character columns are padded to the defined length.
All trailing spaces are removed from variable-length column data, except when a string contains only spaces. Strings that contain only spaces are truncated to a single space. Strings longer than the specified length of a char, nchar, unichar, varchar, univarchar, or nvarchar column are silently truncated unless you set string_rtruncation on.
An update to a text or unitext column initializes the text or unitext column, assigns it a valid text pointer, and allocates at least one text page.