GROUP BY Clause in SQL
The GROUP BY clause in SQL groups rows that share the same values. It is mainly used with aggregate functions such as COUNT, SUM, AVG, MIN, and MAX.
Because of this, GROUP BY helps you summarize data instead of viewing every single row.
Why GROUP BY Clause in SQL Is Used
GROUP BY is useful when you want to
combine similar data
generate summary reports
analyze totals or averages
work with large tables
As a result, it plays an important role in data analysis.
Sample Table Used for GROUP BY
students
id | name | city | marks
1 | Rahul | Delhi | 85
2 | Neha | Mumbai | 92
3 | Amit | Delhi | 78
4 | Priya | Pune | 88
5 | Karan | Mumbai | 90
Basic GROUP BY Example
SELECT city, COUNT(*)
FROM students
GROUP BY city;
This query counts students in each city.
GROUP BY with SUM
SELECT city, SUM(marks)
FROM students
GROUP BY city;
This query shows total marks for each city.
GROUP BY with AVG
SELECT city, AVG(marks)
FROM students
GROUP BY city;
This query calculates average marks per city.
GROUP BY with Multiple Columns
SELECT city, name, AVG(marks)
FROM students
GROUP BY city, name;
This groups data by both city and name.
GROUP BY Clause with WHERE
SELECT city, COUNT(*)
FROM students
WHERE marks > 80
GROUP BY city;
This filters data first and then groups it.
Important Rule of GROUP BY Clause in SQL
Every column in the SELECT list must either
be part of GROUP BY
or use an aggregate function
Ignoring this rule causes errors.
Common Mistake Example
SELECT city, name, AVG(marks)
FROM students
GROUP BY city;
This query fails because name is not grouped.
Real World Use Cases
GROUP BY clause in SQL is commonly used in
sales reports
student performance analysis
banking summaries
inventory tracking
Summary
GROUP BY groups similar rows.
It works with aggregate functions.
It helps summarize large datasets.
Once you understand GROUP BY, reporting becomes much easier.
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