awk to process the first two lines then the next two and so on - bash

Question

Suppose i have a very file which i created from two files one is old & another is the updated file by using cat & sort on the primary key.
File1
102310863||7097881||6845193||271640||06007709532577||||
102310863||7097881||6845123||271640||06007709532577||||
102310875||7092992||6840808||023740||10034500635650||||
102310875||7092992||6840818||023740||10034500635650||||
So pattern of this file is line 1 = old value & line 2 = updated value & so on..
now I want to process the file in such a way that awk first process the first two lines of the file & find out the difference & then move on two the next two lines.
now the process is
if($[old record]!=$[new record])
i= [new record]#[old record];
Desired output
102310863||7097881||6845123#6845193||271640||06007709532577||||
102310875||7092992||6840818#6840808||023740||10034500635650||||

Answer 1

$ cat tst.awk
BEGIN { FS="[|][|]"; OFS="||" }
NR%2 { split($0,old); next }
{
for (i=1;i<=NF;i++) {
if (old[i] != $i) {
$i = $i "#" old[i]
}
}
print
}
$
$ awk -f tst.awk file
102310863||7097881||6845123#6845193||271640||06007709532577||||
102310875||7092992||6840818#6840808||023740||10034500635650||||

Answer 2

This awk could help:
$ awk -F '\\|\\|' '{
getline new;
split(new, new_array, "\\|\\|");
for(i=1;i<=NF;i++) {
if($i != new_array[i]) {
$i = new_array[i]"#"$i;
}
}
} 1' OFS="||" < input_file
102310863||7097881||6845123#6845193||271640||06007709532577||||
102310875||7092992||6840818#6840808||023740||10034500635650||||
I think, you are good enough in awk to understand above code. Skipping the explanation.

Answer 3

Updated version, and thanks #martin for the double | trick:
$ cat join.awk
BEGIN {new=0; FS="[|]{2}"; OFS="||"}
new==0 {
split($0, old_data, "[|]{2}")
new=1
next
}
new==1 {
split($0, new_data, "[|]{2}")
for (i = 1; i <= 7; i++) {
if (new_data[i] != old_data[i]) new_data[i] = new_data[i] "#" old_data[i]
}
print new_data[1], new_data[2], new_data[3], new_data[4], new_data[5], new_data[6], new_data[7]
new = 0
}
$ awk -f join.awk data.txt
102310863||7097881||6845123#6845193||271640||06007709532577||||
102310875||7092992||6840818#6840808||023740||10034500635650||||