Match common IDs between two huge csv files [closed]

Answer 1

Load the information in memory with awk and then print the line if the id matches:

$ awk 'FNR==NR {a[$1]=$2; next} ($1 in a) {print $1, $2, a[$1]}' f2 f1
1 a 002
2 b x90

Explanation

The basic idea is to do things when reading file1 and other_things when reading file2:

awk 'FNR==NR {things; next} {other_things}' file1 file2

In our case, things is to store the content of file2 in memory, mapping every id to its value.

Then, it goes through file1 and prints the content of the line, together with the mapped value, if there is a common id.