汇总数据

AI 助力的 SQL 查询进阶

Jasmin Ludolf

Senior Data Science Content Developer

聚合函数

SUM()
AVG()
MIN()
MAX()

每部电影的平均投票数是多少？

含汇总统计的报告

汇总字段

聚合函数将多行汇总为单个值

便于按整体或分组理解数据

提示： 显示所有电影的投票总数

SELECT SUM(num_votes) AS total_votes
FROM reviews;

|total_votes|
|-----------|
|419507814  |

计算字段平均值

提示： 每部电影的平均投票数是多少？

SELECT AVG(num_votes) AS average_votes_per_film
FROM reviews;

|average_votes_per_film|
|----------------------|
|84441.991545893720    |

四舍五入结果

提示： 每部电影的平均投票数（四舍五入）是多少？

SELECT ROUND(AVG(num_votes)) AS avg_votes
FROM reviews;

|avg_votes|
|---------|
|84442    |

ROUND(AVG(num_votes), 1)

84442.0

ROUND(AVG(num_votes), 2)

84441.99

ROUND(AVG(num_votes), -2)

四舍五入结果

提示： …保留一位小数

SELECT ROUND(AVG(num_votes), 1) AS avg_votes
FROM reviews;

|avg_votes|
|---------|
|84442.0  |

提示： …四舍五入到百位

SELECT ROUND(AVG(num_votes), -2) AS avg_votes
FROM reviews;

|avg_votes|
|---------|
|84400    |

分组平均值

提示： 按语言显示四舍五入后的平均预算，按预算从高到低排序

SELECT language, ROUND(AVG(budget)) AS average_budget
FROM films
GROUP BY language
ORDER BY average_budget DESC;

|language |average_budget|
|---------|--------------|
|Greek    |              |
|Kannada  |              |    
|Polish   |              |
|Korean   |2741550000    |
...

最小值与最大值

提示： 按字母顺序显示各国最低与最高预算

SELECT country, 
       MIN(budget) AS lowest_budget, 
       MAX(budget) AS highest_budget
FROM films
GROUP BY country
ORDER BY country;

|country    |lowest_budget|highest_budget|
|-----------|-------------|--------------|
|Afghanistan|46000        |46000         |
|Argentina  |800000       |2000000       |
|Aruba      |35000000     |35000000      |
...

识别取值范围
理解数据范围
理解典型值

聚合函数与数据类型

仅数值字段

SUM()
AVG()

多种数据类型

MIN()
MAX()
COUNT()

最小 <-> 最大

最低 <-> 最高
A <-> Z
最早 <-> 最新

最小值与最大值

SELECT MIN(language) AS min_language
FROM films;

|min_language|
|------------|
|Aboriginal  |

SELECT MAX(language) AS max_language
FROM films;

|max_language|
|------------|
|Zulu        |

SQL 最佳实践：别名

SELECT SUM(budget) AS total_budget
...

SELECT AVG(budget) AS average_budget
...

SELECT country, 
       MIN(budget) AS lowest_budget, 
       MAX(budget) AS highest_budget
...

SELECT AVG(num_user), AVG(num_critic)
FROM reviews;

|avg     |avg     |
|275.6...|141.9...|

SQL 最佳实践：格式化

多行书写查询
使用缩进

SELECT country, 
       MIN(budget) AS lowest_budget, 
       MAX(budget) AS highest_budget
FROM films
GROUP BY country
ORDER BY country;

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AI 助力的 SQL 查询进阶