Error Code 1111. Invalid use of group function

Question

So this works:

SELECT c.name AS country_name, c.population AS country_population, SUM(ci.population) AS city_population, ROUND(100*(SUM(ci.population)/c.population)) AS city_population_percent
FROM country AS c
JOIN city AS ci
ON c.code = ci.countrycode
WHERE c.continent = 'Europe'
GROUP BY c.name

But I need to only grab the city_population_percent values greater than 30, so I try this:

SELECT c.name AS country_name, c.population AS country_population, SUM(ci.population) AS city_population, ROUND(100*(SUM(ci.population)/c.population)) AS city_population_percent
FROM country AS c
JOIN city AS ci
ON c.code = ci.countrycode
WHERE c.continent = 'Europe'
**AND ROUND(100*(SUM(ci.population)/c.population)) > 30**
GROUP BY c.name

And that's when I get:

Error Code 1111. Invalid use of group function

That is, it fails when I add this condition in the WHERE:

AND ROUND(100*(SUM(ci.population)/c.population)) > 30

Answer 1

So you have to move this condition to the HAVING clause

SELECT c.name AS country_name, c.population AS country_population, SUM(ci.population) AS city_population, ROUND(100*(SUM(ci.population)/c.population)) AS city_population_percent
            FROM country AS c
            JOIN city AS ci
            ON c.code = ci.countrycode
WHERE c.continent = 'Europe'
GROUP BY c.name
HAVING ROUND(100*(SUM(ci.population)/c.population)) > 30

Answer 2

You're using aggregate functions in a where clause, something you cannot do in SQL.

Use the HAVING clause instead:

WHERE c.continent = 'Europe'
GROUP BY c.name
HAVING ROUND(100*(SUM(ci.population)/c.population)) > 30