`mlr join` feature request: if `--lk` is empty keep all left fields about miller HOT 3 CLOSED

@aborruso I believe this already exists -- ?

$ cat a.csv
N,S,T,U
1,a,b,c
2,d,e,f
3,g,h,i

$ cat b.csv
N,X,Y,Z
1,l,m,n
2,o,p,q
3,r,s,t

$ mlr --csv join -j N -f a.csv b.csv
N,S,T,U,X,Y,Z
1,a,b,c,l,m,n
2,d,e,f,o,p,q
3,g,h,i,r,s,t

$ mlr --csv join -j N --lk N -f a.csv b.csv
N,X,Y,Z
1,l,m,n
2,o,p,q
3,r,s,t

$ mlr --csv join -j N --lk "" -f a.csv b.csv
N,X,Y,Z
1,l,m,n
2,o,p,q
3,r,s,t

from miller.

@aborruso I'll add a note to the online help for mlr join

from miller.

@aborruso I'll add a note to the online help for mlr join

These last few issues of mine were all wrong, sorry.

But please add it, because I had no idea that if no field indicated, only the left ones would remain.
I had not even tested it, because I had taken the documentation literally.

Thank you very much

from miller.