In Stata, the “merge” command performs a Full Join by default.

Observations must be dropped to create a Left Join.

* Import the left dataset, referred to as the “master” dataset

use "1to1 left", replace

* Merge the right dataset, referred to as the “using” dataset on the unique identifier Key

merge 1:1 Key using "1to1 right" 

* The following table summarizes the output of _merge variable     created by the merge

* ( _merge == 1) : left join

* ( _merge == 2) : right join

* ( _merge == 3) : inner join

* Drop observations from using dataset

drop if _merge == 2

Alternatively the “joinby” command can also be used.

joinby Key using "1to1 right.dta", unmatched(master)

Functions referenced:

use

merge

drop

joinby

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