怎么把一个值的1,2,6位去掉保留别的数据？求教

有个字段  我取出这个字段里一个值  然后要处理这个值  去掉1,2,6位  然后把前三位四舍五入一下变成两位 例如下面的数据

{"PRODUCT_ID":"TH645AAAB100","PROCESS_ID":"3380","EQP_ID":"THCDO310","PRE PROCESS ID":"3300"}

我需要取出TH645AAAB100 改为65AAB100  求指点

$A = '{"PRODUCT_ID":"TH645AAAB100","PROCESS_ID":"3380","EQP_ID":"THCDO310","PRE PROCESS ID":"3300"}';
$B = json_decode($A,true);
$D = str_split($B['PRODUCT_ID']);
unset($D[0]);
unset($D[1]);
unset($D[5]);

$E = implode('',$D);
$F = mb_substr($E,0,3);
$G = mb_substr($E,3);
$H = round($F/10);
$I = $H.$G;
var_dump($I);//string(8) "65AAB100"

select substr(substr('TH645AAAB100',3,10),1,3),substr(substr('TH645AAAB100',3,10),5,6) from  dual limit 1;

哈 我怎么感觉跟个 面试题似的呢