as poj has already pointed out "I suspect there are other problems" but you have at least successfully identified that you get that error when $feed_table_idcode->fetchrow_array does not return any rows, because then $feed_table_ext_results->execute never gets executed. One way to test if it has returned any rows is to set some sort of flag to false as a default state, and then set it to true if $feed_table_idcode->fetchrow_array did return a row, (and $feed_table_ext_results->execute gets executed). Then you can skip the $feed_table_ext_results>fetchrow_array loop if your flag is still false

for instance $did_ex_flag=0; sets a flag to false, and $did_ex_flag=1; sets it to true, and if ($did_ex_flag) { ...} can be used to test it.

another way, that might be more useful, would be to move the $feed_table_ext_results->fetchrow_array loop to right after the $feed_table_ext_results->execute statement. Of course you now realize the $feed_table_ext_idcode = statement needs to be before that point.