Difference between a Having clause and a Where clause in SQL Server?

Difference between a Having clause and a Where clause?

Having Clause

The HAVING clause used with aggregate functions.

Having Clause Syntax:
 

SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value;

Where Clause

The WHERE clause is used to filter records. The WHERE clause is used to extract only those records that fulfill a specified criterion.

Where Clause Syntax:

SELECT column_name,column_name FROM table_name WHERE column_name operator value;

HAVING Clause Vs WHERE Clause

• Where specify a search condition for a group or an aggregate. But HAVING clause can be used only with the SELECT statement.

• HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause.

• Having Clause is basically used only with the GROUP BY function in a query, whereas WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. 

• Where applies to each and single row, whereas having applies to summarized rows (summarized with GROUP BY) 

• WHERE clause is used for filtering rows and it applies on each and every row, while HAVING clause is used to filter groups in SQL.

• One syntax level difference between WHERE and HAVING clause is that, former is used before GROUP BY clause, while later is used after GROUP BY clause.