筛选分组数据

SQL 中级

Jasmin Ludolf

Data Science Content Developer, DataCamp

HAVING

SELECT 
       release_year,
       COUNT(title) AS title_count
FROM films
GROUP BY release_year
WHERE COUNT(title) > 10;

在 "WHERE" 附近的语法错误
第 4 行: WHERE COUNT(title) > 10;
        ^

SELECT 
       release_year,
       COUNT(title) AS title_count
FROM films
GROUP BY release_year
HAVING COUNT(title) > 10;

|release_year|title_count|
|------------|-----------|
|1988        |31         |
|null        |42         |
|2008        |225        |
...

执行顺序

-- Written code:

SELECT 
       certification, 
       COUNT(title) AS title_count
FROM films
WHERE certification 
       IN ('G', 'PG', 'PG-13')
GROUP BY certification
HAVING COUNT(title) > 500
ORDER BY title_count DESC
LIMIT 3;

-- Order of execution:

SELECT 
       certification, 
       COUNT(title) AS title_count

FROM films

WHERE certification 
       IN ('G', 'PG', 'PG-13')

GROUP BY certification

HAVING COUNT(title) > 500

ORDER BY title_count DESC

LIMIT 3;

HAVING 与 WHERE

WHERE 过滤行，HAVING 过滤分组
2000 年上映了哪些电影？

SELECT title
FROM films
WHERE release_year = 2000;

|title         |
|--------------|
|102 Dalmatians|
|28 Days       |
...

哪些年份的平均片长超过两小时？

HAVING 与 WHERE

哪些年份的平均片长超过两小时？

SELECT release_year
FROM films

GROUP BY release_year

HAVING AVG(duration) > 120;

|release_year|
|------------|
|1954        |
|1959        |
...

Let's practice!

SQL 中级