The relationship between groupby and having in mysql

GROUP BY After grouping the data, the HAVING clause filters the grouping and only retains the groups that meet the conditions. The two are used together to group data, aggregate data, filter groupings, analyze data, find patterns and trends, summarize information and create statistical reports.

The relationship between GROUP BY and HAVING clauses in MySQL

GROUP BY clause

• Group identical rows together to form a grouped set.
• Used to perform aggregation operations on data, such as SUM(), COUNT(), AVG(), etc.
• The HAVING clause can only be used after the GROUP BY clause.

HAVING clause

• Filters the grouped data and only retains groups that meet specific conditions.
• The HAVING clause must reference a grouping column or aggregate function in GROUP BY.

The relationship between the two

The GROUP BY clause defines the grouping method, while the HAVING clause specifies the filtering conditions after grouping. The combination of these two clauses allows the following operations on the data:

• Grouping data
• Aggregating groups
• Filtering groups that do not meet the conditions

Example

<code class="sql">SELECT department_id, SUM(salary)
FROM employee
GROUP BY department_id
HAVING SUM(salary) > 10000;</code>

• This query first groups employees by department number (department_id).
• Then, it calculates the total salary for each department.
• Finally, the HAVING clause only retains departments where the total salary exceeds 10,000.

Usage scenarios

GROUP BY and HAVING clauses are often used in the following situations:

• Analysis has multiple data Set of data
• Find patterns and trends
• Filter and summarize specific information
• Create statistical reports

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