SQL错误[42703]：错误:列"percent_population_infected“不存在

Question

当我试图从查询中排除空值时，我很难理解弹出的这个错误。谢谢!

/* Looking at countries with Highest Infection Rate compared to Population */

SELECT LOCATION, population,
       MAX(total_cases) AS highest_infection_count,
       MAX((total_cases/population))*100 AS percent_population_infected
FROM public.Covid_deaths
WHERE percent_population_infected IS NOT NULL 
GROUP BY LOCATION, population
ORDER BY percent_population_infected DESC;

SQL Error [42703]: ERROR: column "percent_population_infected" does not exist

Answer 1

对受感染人口百分比别名的限制不属于WHERE子句，它属于HAVING子句。此外，我认为您只想断言给定的位置具有非零的Covid案例计数。把所有这些放在一起：

SELECT
    LOCATION,
    population,
    MAX(total_cases) AS highest_infection_count,
    MAX(total_cases / population)*100 AS percent_population_infected
FROM public.Covid_deaths
GROUP BY LOCATION, population
HAVING MAX(total_cases) > 0
ORDER BY percent_population_infected DESC;