Cannot Truncate and Drop Tables in SQLite

I have used SQLite.swift plugin to drop tables and truncate the tables, but it does not work in device. The code can be executed by simulator, but not ios devices:

            for row in db.prepare("SELECT name FROM sqlite_master WHERE type='table' and name != 'sqlite_sequence'")
            {
                let tableName = row[0] as String
                tableName_container.append(tableName);
            }
            for item in tableName_container {
                db.scalar("DELETE FROM '"+item+"'")
//                db.scalar("DROP TABLE IF EXISTS "+item+";")
            }
            for item in tableName_container {
                db.scalar("DROP TABLE IF EXISTS '"+item+"'")
            }
//            db.scalar("DROP TABLE event")
            for row11 in db.prepare("SELECT name FROM sqlite_master WHERE type='table' and name != 'sqlite_sequence'")
            {
                let tmp_col = row11[0] as String
                let count = db.scalar("Select count(*) From "+tmp_col+" ;")
                println(count)
            }