Difference between Having clause and Group by clause

1. Having Clause :

Having Clause is basically like the aggregate function with the GROUP BY clause. The HAVING clause is used instead of WHERE with aggregate functions. While the GROUP BY Clause groups rows that have the same values into summary rows. The having clause is used with the where clause in order to find rows with certain conditions. The having clause is always used after the group By clause.  

SELECT COUNT (SALARIES) AS COUNT_SALARIES, EMPLOYEES
FROM EMPLOYEES
GROUP BY SALARIES
HAVING COUNT(SALARIES) > 1; 

Advantages:

• It allows for the filtering of groups based on a condition that involves an aggregate function.
• It can be used to perform calculations on aggregated data, such as calculating percentage or ratios.
• It can be used with complex queries to obtain more specific results.

Disadvantages:

• It can slow down query performance if the query involves complex calculations.
• It can be difficult to understand the output of a complex HAVING query.
• It may require subqueries or temporary tables to achieve certain types of filtering.

2. Group By Clause :

The GROUP BY clause is often used with aggregate functions (MAX, SUM, AVG) to group the results by one or more columns or In simple words we can say that The GROUP BY clause is used in collaboration with the SELECT statement to arrange required data into groups. 
The GROUP BY statement groups rows that have the same values. This Statement is used after the where clause. This statement is often used with some aggregate function like SUM, AVG, COUNT atc. to group the results by one or more columns.  

SELECT COUNT (SALARIES) AS COUNT_SALARIES, EMPLOYEES
FROM EMPLOYEES
GROUP BY SALARIES; 

Advantages:

• It allows for the grouping of rows that have the same values in one or more columns.
• It helps to reduce the number of rows in the output table and summarize data.
• It can be used with aggregate functions such as SUM, COUNT, AVG, MIN, MAX, etc., to compute summary statistics for each group.
• It allows for grouping based on multiple columns.

Disadvantages:

• It can be time-consuming to write and optimize complex GROUP BY queries.
• It may require subqueries or temporary tables to achieve certain types of aggregations.
• It can be difficult to understand the output of a complex GROUP BY query.

Similarities  between Having clause and Group by clause : 

• Both the GROUP BY and HAVING clauses are used to summarize data in SQL queries.
• They are used in conjunction with each other to group and filter data based on summary results.
• They can be used to perform calculations on aggregated data.

Difference between Having clause and Group by clause :

S.No.	Having Clause	GroupBy Clause
1.	It is used for applying some extra condition to the query.	The groupby clause is used to group the data according to particular column or row.
2.	Having cannot be used without groupby clause,in aggregate function,in that case it behaves like where clause.	groupby can be used without having clause with the select statement.
3.	The having clause can contain aggregate functions.	It cannot contain aggregate functions.
4.	It restrict the query output by using some conditions	It groups the output on basis of some rows or columns.

Conclusion:

The “Group By” clause is used to group data into summary rows based on common values, while the “Having” clause is used to filter those groups based on a condition that applies to the aggregated data. By understanding the differences between these two clauses, you can write more powerful SQL queries that extract meaningful insights from your data.