import excel "连续五年+-+副本.xls", sheet("Sheet1") firstrow clear //放你的路径
keep code year LNX
scalar i = 2013 //假设A = 2013
keep if year >= i
gen sign = ( LNX!=0)
bysort code: egen treat = mean(sign)
keep if treat == 1 | treat == 0
duplicates drop code,force
save "sign.dta",replace

import excel "连续五年+-+副本.xls", sheet("Sheet1") firstrow clear
keep code year LNX
merge m:1 code using "sign.dta",keepusing(treat)
keep if _merge == 3
drop _merge
gen post = (year >= i & treat ==1)