Objective  : Merge the contents of two files using common key present in the files

 file1.txt
 =========
 key1   11
 key2   12
 key3   13


 file2.txt
 =========
 key2   22
 key3   23
 key4   24
 key5   25


 Expected Output :
 ==================
 key1   11
 key2   12    22
 key3   13    23 
 key4   24
 key5   25

Approaches Tried :

1. Tried join command

    join -a 1 -a 2 file1.txt file2.txt ## full outer join
   

2. Using awk

    awk 'FNR==NR{a[$1]=$2;next;}{ print $0, a[$1]}' 2.txt 1.txt
   

Approach 2 is resulting in right outer join and NOT full outer join

   key1  11
   key2  12    22
   key3  13    23 
 

What needs to be modified in approach 2 which will result in full outer join?

Objective: Merge the contents of two files using common key present in the files

 file1.txt
 =========
 key1   11
 key2   12
 key3   13


 file2.txt
 =========
 key2   22
 key3   23
 key4   24
 key5   25


 Expected Output :
 ==================
 key1   11
 key2   12    22
 key3   13    23 
 key4   24
 key5   25

Approaches tried:

1. join command:

    join -a 1 -a 2 file1.txt file2.txt ## full outer join
   

2. awk:

    awk 'FNR==NR{a[$1]=$2;next;}{ print $0, a[$1]}' 2.txt 1.txt
   

Approach 2 is resulting in a right outer join and NOT a full outer join:

   key1  11
   key2  12    22
   key3  13    23 
 

What needs to be modified in approach 2 to result in a full outer join?

Objective : Merge the contents of two files using common key present in the files

 file1.txt
 =========
 key1   11
 key2   12
 key3   13


 file2.txt
 =========
 key2   22
 key3   23
 key4   24
 key5   25


 Expected Output :
 ==================
 key1   11
 key2   12    22
 key3   13    23 
 key4   24
 key5   25

Approaches Tried :

1. Tried join command

    join -a 1 -a 2 file1.txt file2.txt ## full outer join
   

2. Using awk

    awk 'FNR==NR{a[$1]=$2;next;}{ print $0, a[$1]}' 2.txt 1.txt
   

Approach 2 is resulting in right outer join and NOT full outer join

   key1  11
   key2  12    22
   key3  13    23 
 

Questions :

1. What needs to be modified in approach 2 which will result in full outer join ?
2. Which would be the better approach (#1 or #2) when we have lot of key-value pairs in files (file size of GB/TB)

Any inputs/ thoughts on the above questions is much appreciated thanks.

Objective : Merge the contents of two files using common key present in the files

 file1.txt
 =========
 key1   11
 key2   12
 key3   13


 file2.txt
 =========
 key2   22
 key3   23
 key4   24
 key5   25


 Expected Output :
 ==================
 key1   11
 key2   12    22
 key3   13    23 
 key4   24
 key5   25

Approaches Tried :

1. Tried join command

    join -a 1 -a 2 file1.txt file2.txt ## full outer join
   

2. Using awk

    awk 'FNR==NR{a[$1]=$2;next;}{ print $0, a[$1]}' 2.txt 1.txt
   

Approach 2 is resulting in right outer join and NOT full outer join

   key1  11
   key2  12    22
   key3  13    23 
 

What needs to be modified in approach 2 which will result in full outer join?