sql 語句問題？

[xiayule]

select t3.cust_no, t3.cust_name, left(t1.part_no, 2) as fpart,'三极管TO-92封裝' as ftype, sum(t1.qty) as fqty, sum(round(t1.amt, 2)) as famt
from s_invoice_dt t1
inner join s_invoice_hd t2 on t1.inv_no = t2.inv_no
inner join customer t3 on t2.cust_no = t3.cust_no
where left(part_no, 2) = '03' and substring(t1.part_no,5,1) = 'A' and t2.posted = 1 and t2.cy_id = 'RMB' and t3.cust_no in ('SCM00001,SCM00003,SCQ00007')
group by t3.cust_no, t3.cust_name, left(t1.part_no, 2)

查詢結果為空，如果将上述的t3.cust_no in ('SCM00001,SCM00003,SCQ00007')换成t3.cust_no='SCM00001' or t3.cust_no='SCM00003' or t3.cust_no='SCQ00007'就可以查询到5条记录，为什么？