> update tablea set a=10-$inputstring where key=1;
Add parenthesis:
update tablea set a=10-($inputstring) where key=1;
Thus you get :
update tablea set a=10-(-1) where key=1;
instead of :
update tablea set a=10--1 where key=1;
You'd have a problem because -- is the Comment Delimiter thus
update tablea set a=10--1 where key=1;
means :
update tablea set a=10;
which does update all rows.
I still think inputstring should be cast to int in YOUR code prior to be
sent to SQL, because then you can give a good error message to the user
instead of "SQL request failed".
