How can I find the number of rivers that only are in one country?-CodePudding

I need to use MySQL to find how many rivers are only in one country. Basically counting the numbers that are never duplicated

riverID  Country
1   BI
1   CD
1   EG
1   ER
1   ET
1   KE
1   RW
1   SD
1   SS
1   TZ
1   UG
2   BO
2   BR
2   CO
2   EC
2   GY
2   PE
2   VE
3   CN
4   CA
4   US
5   MN
5   RU
6   CN
7   CN
7   KZ

CodePudding user response：

You need to use GROUP BY and COUNT.

Maybe that SQL Query may help you :

select count(riverId)
from your_table
group by Country

CodePudding user response：

SELECT riverID, COUNT(*) AS num_countries
FROM table
GROUP BY riverID
HAVING num_countries = 1