The `GROUP BY` clause with the `HAVING` clause is an important feature of SQL used for organizing, grouping, and filtering data in a relational database. In Database Management Systems, databases usually contain large amounts of information stored in tables. SQL provides various clauses to retrieve meaningful information from these tables. The `GROUP BY` clause is used to arrange rows having the same values into groups, while the `HAVING` clause is used to filter these groups according to a specified condition. Together, they are especially useful when aggregate functions such as `COUNT()`, `SUM()`, `AVG()`, `MAX()`, and `MIN()` are applied to grouped data. The `GROUP BY` clause divides the rows of a table into groups based on one or more columns. Rows having the same value in the specified column or columns are placed in the same group. Aggregate functions can then be applied to each group separately. For example, suppose there is an `Employee` table containing the columns `Employee_ID`, `Employee_Name`, `Department`, and `Salary`. If we want to find the total salary paid to employees in each department, we can use: ```sql SELECT Department, SUM(Salary) FROM Employee GROUP BY Department; ``` In this query, employees are grouped according to their department. The `SUM()` function then calculates the total salary for each department. Thus, instead of displaying individual employee records, the query produces one result for each department. The general syntax of the `GROUP BY` clause is: ```sql SELECT column1, aggregate_function(column2) FROM table_name GROUP BY column1; ``` More than one column can also be specified in the `GROUP BY` clause. For example: ```sql SELECT Department, Job_Title, AVG(Salary) FROM Employee GROUP BY Department, Job_Title; ``` Here, employees are grouped first according to department and then according to job title within each department. The average salary is calculated for every department-job title combination. The `HAVING` clause is used to apply conditions to groups created by the `GROUP BY` clause. It is particularly useful when the condition involves an aggregate function. For example, suppose we want to display only those departments where the total salary is greater than ₹500,000: ```sql SELECT Department, SUM(Salary) AS Total_Salary FROM Employee GROUP BY Department HAVING SUM(Salary) > 500000; ``` The `GROUP BY` clause first creates groups based on departments. The `SUM(Salary)` function calculates the total salary for every department. The `HAVING` clause then retains only those departments whose total salary is greater than ₹500,000. The main difference between `WHERE` and `HAVING` is an important concept in SQL. The `WHERE` clause filters individual rows before grouping takes place, whereas the `HAVING` clause filters groups after grouping and aggregation have taken place. For example: ```sql SELECT Department, AVG(Salary) FROM Employee WHERE Salary > 30000 GROUP BY Department HAVING AVG(Salary) > 50000; ``` In this query, the `WHERE` clause first removes employees whose salary is ₹30,000 or less. The remaining employees are then grouped according to department. The average salary is calculated for each department, and the `HAVING` clause keeps only those departments whose average salary exceeds ₹50,000. The logical processing of such a query can therefore