Скачать или смотреть GROUP BY and Aggregate Functions in MySQL

In this SQL GROUP BY video, you will see a table full of university students. Such data is frequently used to calculate statistics by using the SQL GROUP BY clause and other SQL clauses.
Given that we have student names (StudentName), subjects (Subject), scores (Score), and the semesters they've studied (Semester), we can use that data and employ the SQL GROUP BY clause to organize and aggregate data based on one or more columns.
The SQL GROUP BY statement can also be used with aggregate functions like COUNT, SUM, AVG, MIN, or MAX.

To calculate average student scores per subject, we'd use an SQL GROUP BY query as follows:
SELECT Subject, ROUND(AVG(Score,2) AS AverageScore from students GROUP BY Subject;

To calculate the number of students per semester, we'd use the following SQL GROUP BY query together with the SQL GROUP BY and COUNT functions:
SELECT Semester, COUNT(*) AS NumberOfStudents FROM students GROUP BY Semester;

We can also write similar SQL GROUP BY statement using SQL GROUP BY and HAVING clause or the SQL GROUP BY and ORDER BY clauses.

To calculate the highest score per subject, we can use an SQL GROUP BY with examples SQL query as follows:
SELECT Subject, MAX(Score) AS HighestScore FROM students GROUP BY Subject;

In the first query, we've used the SQL ROUND function to display 2 numbers after the dot.

The crux of the SQL GROUP BY clause is that we select something (SELECT column), then generally use an SQL aggregate function like COUNT, SUM, AVG, MIN, or MAX, and then utilize the GROUP BY clause to group everything by a column.

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