Hi,
I am new to Stata 15 and I need some help.

I have two databases (database_y and database_x). I have 4 variables that are named the same (year, product, code of province origin and code of region origin) in both databases.
In the database_y I have additional information (it gives me the destination of the provinces and regions of origin). So, I just wanted to merge both databases in order to have the source information and to add the destination provinces/regions.
I have tried to make a merge, but I have an answer from Stata: variable year product o_province_code o_region_code does not uniquely identify observations in the master/using data r(459);
I have looked at some examples on the forum and none have solved my problem.
* Database_x
* Example generated by -dataex-. To install: ssc install dataex
clear
input str4 year str2(product o_province_code) byte(o_region_code o_customs_code) double(tm_exports_x vm_exports_x)
"2010" "01" "8" 9 8 .35 696
"2010" "01" "43" 9 11 .8 5000
"2010" "04" "41" 1 11 .168 150
"2010" "05" "31" 15 11 .104 3058.14
"2010" "05" "11" 1 11 .18 1920
"2011" "01" "46" 10 11 .043000000000000004 1450
"2011" "01" "43" 9 11 .2 350
"2011" "01" "41" 1 11 .55 9840
"2011" "05" "31" 15 11 1.437 38284.23
"2012" "01" "11" 1 11 .55 2000
"2012" "03" "15" 12 15 .106 10051.49
"2012" "03" "28" 13 11 .3 3420
"2012" "04" "26" 17 11 .026 156.23
"2012" "04" "19" 8 11 .192 391.8
"2012" "05" "43" 9 11 .794 10875.91
"2012" "05" "25" 9 11 1.239 5940
"2013" "01" "4" 1 4 .45 1800
"2013" "01" "15" 12 11 .5 3700
"2014" "01" "43" 9 11 .171 14726
"2015" "01" "46" 10 11 .6 1000
"2015" "01" "29" 1 11 .8 2200
"2015" "02" "24" 7 11 .121 2150
"2015" "03" "3" 10 3 .99 20195
"2015" "05" "18" 1 46 .8 6840
"2015" "05" "31" 15 8 4.106 7672.18
"2016" "01" "28" 13 11 .036 930
"2016" "01" "15" 12 11 .168 238
"2016" "02" "2" 8 11 .097 2657.05
"2016" "02" "37" 7 11 .12 1029.67
"2016" "03" "29" 1 11 .096 379.2
"2016" "03" "17" 9 11 .977 22867
"2016" "05" "33" 3 11 .216 270
"2016" "05" "28" 13 11 .8 247.98
"2017" "01" "30" 14 11 .6 9000
"2017" "01" "29" 1 11 .825 60
"2017" "02" "37" 7 11 .172 1796.7799999999997
"2017" "02" "24" 7 11 .235 3917.43
"2017" "02" "25" 9 11 .296 3109.67
"2017" "04" "12" 10 11 .003 19.02
"2017" "04" "45" 8 8 .15 405
"2017" "05" "31" 15 8 3.424 14424.9
"2018" "02" "24" 7 11 .102 1794.04
"2018" "02" "25" 9 11 .208 1543.06
"2018" "03" "3" 10 3 .4 5750
"2018" "03" "43" 9 11 .432 915.84
"2018" "03" "18" 1 11 .9 3253.45
"2018" "04" "29" 1 46 .12 660
"2018" "04" "2" 8 11 .213 2814.06
end
*Database y
* Example generated by -dataex-. To install: ssc install dataex
clear
input str4 year str2(product o_province_code) byte o_region_code int d_province_code byte d_region_code long exports_tm_y
"2010" "03" "11" 1 1 9 .
"2010" "03" "35" 5 1 9 148
"2010" "03" "P8" 9 1 9 .
"2010" "03" "46" 10 1 9 12
"2010" "03" "36" 12 1 9 155
"2011" "03" "11" 1 1 9 7
"2011" "03" "29" 1 1 9 .
"2011" "03" "35" 5 1 9 97
"2011" "03" "P8" 9 1 9 .
"2011" "03" "36" 12 1 9 57
"2014" "08" "11" 1 141 6 .
"2014" "08" "P8" 9 141 6 1
"2016" "08" "11" 1 141 6 .
"2010" "08" "35" 5 321 11 18
"2010" "08" "P4" 1 381 2 195
"2011" "08" "P4" 1 381 2 116
"2012" "10" "46" 10 1 9 22
"2013" "10" "11" 1 1 9 .
"2013" "10" "35" 5 1 9 .
"2013" "10" "P8" 9 1 9 .
"2013" "10" "46" 10 1 9 .
"2014" "10" "11" 1 1 9 .
"2015" "10" "11" 1 1 9 .
"2010" "25" "P3" 10 1 9 35028
"2010" "25" "46" 10 1 9 572
"2010" "25" "36" 12 1 9 69
"2010" "25" "48" 16 1 9 46
"2011" "25" "11" 1 1 9 .
"2011" "25" "35" 5 1 9 .
"2011" "25" "P8" 9 1 9 48
"2011" "25" "46" 10 1 9 164
end

I will be grateful for any help you can provide