Shell Programming and Scripting

A AB 3.7
B AB 2.5

A AB 3.5
A AB 3.7

A AB 3.7 2
B AB 2.5 0

awk 'NR==FNR{a[$1$2]++;next} {if (a[$1$2]){print $0,a[$1$2]}else {print $0,"0"}}' File2 File1

awk -F '\t' '
  NR==FNR{
    A[$1 OFS $2]=$3
    C[$1 OFS $2]=0
    next
  } 
  $3<=A[$1 OFS $2]{
    C[$1 OFS $2]++
  } 
  END{
    for(i in A)print i,A[i],C[i]
  }
' file1 file2

awk 'BEGIN{SUBSEP=FS} FNR==NR{a[$1,$2]=$3;next} {
for(i in a){
if($1SUBSEP$2==i) {
if($3<=a[i]) {
b[i]++;break}}}
} END{for(i in a) printf("%s %s %d\n",i,a[i],b[i])}' file1 file2

A[A AB]=3.7 etc
C[A AB]=0
Now here index is field 1 and 2.
 
When printing in for loop how system decide the value of var i whether it should be variable or string [A AB].