在sqlite中更新语句

sqlite3_stmt *updateStmt = nil;
    if (updateStmt == nil) 
    {
        const char *sql = " update PPM set amount = ? ";
        if (sqlite3_prepare_v2(appDelegate.PPMdatabase, sql, -1,&updateStmt, NULL)!= SQLITE_OK)
        {
            NSAssert (0,@"Error while creating update statement. '%s'",sqlite3_errmsg(appDelegate.PPMdatabase));
        }
    }
    sqlite3_bind_double (updateStmt,1, Val);
if (SQLITE_DONE != sqlite3_step(updateStmt))
    {
        NSAssert(0,@"Error while updating.'%s'",sqlite3_errmsg(appDelegate.PPMdatabase));
    }
    sqlite3_reset(updateStmt);