sql-aggregate-functions-example

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SQL Aggregate Functions Explained with Tables

Students Table

ID	Name	Age	Class	Score
1	张三	18	A班	85
2	李四	19	B班	92
3	王五	20	A班	78
4	赵六	18	B班	96
5	钱七	21	A班	88

Aggregate Functions Examples

1. COUNT()

sql

SELECT COUNT(*) AS Student Count FROM Students;

Result:

Student Count
5

2. AVG()

sql

SELECT Class, AVG(Age) AS Average Age
FROM Students
GROUP BY Class;

Result:

Class	Average Age
A班	19.67
B班	18.5

3. SUM()

sql

SELECT Class, SUM(Score) AS Total Score
FROM Students
GROUP BY Class;

Result:

Class	Total Score
A班	251
B班	188

4. MAX()

sql

SELECT Class, MAX(Score) AS Highest Score
FROM Students
GROUP BY Class;

Result:

Class	Highest Score
A班	88
B班	96

5. MIN()

sql

SELECT Class, MIN(Age) AS Minimum Age
FROM Students
GROUP BY Class;

Result:

Class	Minimum Age
A班	18
B班	18

6. Using HAVING

sql

SELECT Class, AVG(Score) AS Average Score
FROM Students
GROUP BY Class
HAVING AVG(Score) > 85;

Result:

Class	Average Score
B班	94

This query shows only the classes with an average score higher than 85.