clear all
sysuse auto

preserve
keep make mpg
save "mpg", replace

restore
keep make weight
save "weight", replace

clear all
use "mpg"

merge 1:1 make using "weight" 

* not all observation match
clear all
sysuse auto

preserve
keep make mpg
keep in 1/10
save "mpg", replace

restore
keep make weight
keep in 5/74
save "weight", replace

clear all
use "mpg"
merge 1:1 make using "weight" 

* some variables that aren't key, but have the same name
clear all
sysuse auto

keep in 1/15

preserve
keep make price mpg
replace price = 1000
save "mpg", replace

restore
keep make price  weight
save "weight", replace

clear all // checking version
use "mpg"
merge 1:1 make price using "weight" 

clear all // I know "weight" prices are good version
use "weight"
merge 1:1 make using "mpg"