SQL 处理子查询错误代码：1111

Question

我正在尝试学习一些 SQL，所以我一直在摆弄示例世界架构。对于此查询，目标是针对每个大陆检索预期寿命高于该大陆平均寿命的国家/地区的首都。

下面的代码是我的尝试，但我在 where 语句中收到 1111 错误。任何帮助将不胜感激！

SELECT continent AS Continent,
       city.name AS Capital
FROM city,
     country c1
WHERE c1.capital = city.id
  AND avg(LifeExpectancy) <
    (SELECT avg(LifeExpectancy)
     FROM country c2
     WHERE c2.continent = c1.continent );

Answer 1

根据你的问题陈述，你不需要首都的平均预期寿命，只需要与首都对应的国家的预期寿命大于该大陆的平均预期寿命。因此，我在下面的查询中进行了这些调整。

让我知道这有效。

SELECT continent AS Continent,
       city.name AS Capital
FROM city,
     country c1
WHERE c1.capital = city.id
  AND c1.LifeExpectancy >
    (SELECT avg(LifeExpectancy)
     FROM country c2
     WHERE c2.continent = c1.continent );

Answer 2

您必须正确地将表 country 和 city 连接到一个查询，该查询 returns 每个大陆的平均值 lifeexpectancy：

select co.code, ci.name
from country co
inner join city ci on ci.id = co.capital
inner join (
  select continent, avg(lifeexpectancy) avg_lifeexpectancy
  from country
  group by continent
) t on t.continent = co.continent and t.avg_lifeexpectancy < co.lifeexpectancy

SQL 处理子查询错误代码：1111

SQL dealing with subqueries Error Code: 1111

mysql

sql

mysql-error-1111