Linux - join 2 CSV files

Question

I have 2 CSV files:

file_1 columns: id,user_id,message_id,rate
file_2 columns: id,type,timestamp

The relation between the files is that

Answer 1

You can try this:
1. Change all lines to start with the key:

awk -F',' { print $3 " file1 " $1 " " $2 " " $4 } < file1 >  temp
awk -F',' { print $1 " file2 " $2 " " $3 }        < file2 >> temp

Now the lines look like:

message_id file1 id user_id rate
id file2 type timestamp

1. Sort temp by the first two columns. Now related lines are adjacent, with file1 first

   sort -k 1,1 -k 2,2 < temp > temp2

2. Run awk to read the lines. In file1 lines save the fields, in file2 lines print them.