how to make jdbc adapter Synchronous in PI

problem:

i have an scenario where I am sending data fromjdbc adapter(oracle DB) to RFC ,now it is asynchronous,the problem is zhe sender adpter may updater more data than we want ,

my sender adapter :

the query sql ---- 'select * from ztable where flag = 0',

update sql ------''updater ztable set flag = 1 where flag = 0

reason:

firstly execute the query sql,at the same time new data with flag = 0 were putted in the table,but i dont get it,and then secondly,execute update sql,make its flag back 1,and I will never get it .

help me:

what can i do to solve this problem? make the interface synchronous ? .

thank you very much~