Where vs Having

Difference Between Where and Having

The WHERE and HAVING clauses in SQL are used to filter records stored in tables in the databases. The dissimilarities between the WHERE and HAVING clause is a frequent doubtone might have. The fundamental dissimilarities between them are:

• The WHERE clause is used to set out a condition for clearing records before any groupings are categorized.
• The HAVING clause is used to set out a condition for clearingrecords from a group.

Each of the two clausesis discussed in detail in below section.

WHERE Clause

The WHERE clause in MySQL is used withqueries to sort the data from the table. It defines a particular condition when fetching records from a table or multiple tables. If the particular condition is met, only then it returns the value.

The WHERE clause is also capable of implementing the logical connectives. They are also referred to as the Boolean condition that must be true to fetch the data.

SELECT column_name,      
FROM table_name   
WHERE conditions   
GROUP BY column_name;    

The following is the syntax of the WHERE clause:

Example:

Let’s consider the following Employees table.

Emp_id	Name	Gender	Hours
101	Bryan	M	12
103	Mike	M	10
104	Daren	F	5
105	Marie	F	8
106	Marco	M	9
107	Daren	F	12
108	Mike	M	10
109	Marco	M	6
110	Bryan	M	5

SELECT * FROM Employees WHERE Hours > 9;

Query:

The above query will return all the records of those employees who have worked for more than 9 hours.

Output:

Emp_id	Name	Gender	Hours
101	Bryan	M	12
103	Mike	M	10
107	Daren	F	12
108	Mike	M	10

The WHERE clause can also be used with the GROUP BY clause. If this same query is used with the GROUP BY clause, it will give a different result.

Query:

SELECT * FROM 
Employees WHERE 
Hours > 9 
GROUP BY Name;

Output:

Emp_id	Name	Gender	Hours
101	Bryan	M	12
103	Mike	M	10
107	Daren	F	12

HAVING Clause

The HAVING clause in MySQL is used along with the GROUP BY clause, and this enables users to specify conditions that filter which group results appear in the result. The WHERE and HAVING clausescan be used in a combined manner as well. In such cases, the WHERE clause sorts the data from each row, and then these rows are grouped. After that, calculations are performed on the groups, and lastly, the HAVING clause operates on these groups.

The following is the syntax for the WHERE clause:

SELECT column_name, 
aggregate_function (expression) 
FROM table_name 
WHERE conditions GROUP BY 
column_name HAVING condition;  

Example:

Let’s consider the same Employees table.

Emp_id	Name	Gender	Hours
101	Bryan	M	12
103	Mike	M	10
104	Daren	F	5
105	Marie	F	8
106	Marco	M	9
107	Daren	F	12
108	Mike	M	10
109	Marco	M	6
110	Bryan	M	5

SELECT name, 
SUM(Hour) 
FROM employees 
GROUP BY name 
HAVING SUM(Hour) > 6;

Query:

The above query will return the name and the total working hours of all the employees who have worked for more than 6 hours.

Output:

Name	Hours
Bryan	17
Mike	20
Daren	17
Marie	8
Marco	15

Difference table between WHERE and HAVING

The key differences between the WHERE clause and the HAVING clause in SQL are listed below in a tabular manner.

WHERE Clause	HAVING Clause
This clause sorts each row.	This clause sorts the groups.
This clause is utilized while performing row operations.	This clause is utilized while performing column operations.
This clause returns the data from rows based on the given condition	This clause returns the complete data and then sorts it according to the given condition.
Aggregate functions cannot be used with this clause.	Aggregate functions can be used with this clause.
This clause can be used with the SELECT, UPDATE, and DELETE statements.	This clause can be used only with the SELECT statement.
The GROUP BY succeeds the WHERE clause.	The GROUP BY clause precedes the HAVING clause.

Conclusion

Both these clauses perform similar ways in sorting out the data, although some specific extra features make the HAVING clause more sought after. One can use aggregate functions while querying data using the HAVING clause while such options are not there for the WHERE clause.