merging two files according to a common column and add 0 to those which are not present in file 2

Question

I would like to merge two files, which share some common data. File 1 includes more than file 2. I want to merge the files based on their shared column following the order of file 1 and I want to add 0 to column 5 (AN1) when the variable is not present in file 2.

My files look like this: File 1

CHR BP  SNP CM  base
20  61098   rs6078030   -0.00024510777  1
20  61795   rs4814683   0   1
20  63231   rs6076506   0.0005026053    1
20  63244   rs6139074   0.00050714752   1

File 2

CHR BP  SNP CM  AN1
20 9836704 rs221007 0 1
20 9817032 rs221011 0 1
20 9764069 rs2206484 0 1
20 9639395 rs4816159 0 1

I want to match them based on column 3 (SNP). I want to keep all the other columns for now.

My desired output would look like this (0 when rsX is not present):

File 3

CHR BP  SNP CM  base AN1
20  61098   rs6078030   -0.00024510777  1   1
20  61795   rs4814683   0   1   1
20  63231   rs6076506   0.0005026053    1   1
20  63244   rs6139074   0.00050714752   1   1

I figured that I need to do this in more than 1 step. I tried to use awk to to the first step but it only creates empty files.

awk -F' ' 'NR==FNR{e[$1$2]=1;next};e[$1$2]' file1 file 2 > file 3
awk -F' ' 'NR==FNR{e[$1$2]=1;next};e[1$2]' file2 file 1 > file 3

I guess the last step will be join file1 file 2 > file 3.

Answer 1

awk 'NR==FNR{ snp[$3]; next }
{ $6=($3 in snp)?(FNR==1?"AN1":"1"):"0" }1' file2 file1