如何解决android.database.sqlite。SQLiteException:没有此类列:ttd(代码1)

i have one database and one table with 85 fields, when i want to add one column named :"ttd", i got an eror, when i delete "ttd" there is no eror, i have check my code, but i think nothing eror, this is my code :i have one database and one table with 85 field