Unknown column 'a.root_id' in 'where clause'解决方法

最近遇到一个问题，

update  sy_user as a inner join sy_user_charge_log as b on b.username=a.username set reconciliation =0 where root_id = 26 and  time between '2016-12-05 14:59:05' and '2016-12-23 18:36:57';

sql运行无问题，可是在thinkphp里面的时候，就报错了1054：Unknown column 'a.root_id' in 'where clause'

后来看到一个文说的是因为运行的时候root_id的个数还没有查出来，导致报错

所以修改了下 sql语句，where分两次写出来，完美运行

$ch->alias('r')->join('__USER__ a on a.username=r.username')->where("root_id='$root_id'")->where("(status = '1') and (reconciliation = '0') and (time between '$start' and '$end')")->field('reconciliation')->save($map);