第一次合并：
use "D:\小论文\结果\企业DVAR2006-2013（清洗后）.dta"
sort name year
save data1,replace

use "D:\小论文\数据\企业数据\2006.dta"
sort name year
save data2,replace

use data1,clear
merge 1:m year name using data2,keepusing(total_asset operating_income employee fix_asset liability open_year)
keep if _merge==3
drop _merge
save data1,replace


第二次合并：

use "D:\小论文\结果\data1.dta"
drop _merge
sort city_code year
duplicates list //列出重复值
duplicates drop
save data1,replace

use  "D:\小论文\结果\firm.dta"
destring year city_code gdp finance industry2 industry3 internet, replace
sort year  city_code
duplicates list //列出重复值
duplicates drop year city_code,force
save firmdata,replace

use data1,clear
merge 1:m year city_code using firmdata,keepusing(gdp finance industry2 industry3 internet )
keep if _merge==3
drop _merge
save data1,replace