Top 5 Amazing difference HAVING vs WHERE SQL

In this article, we delve into the differences between HAVING vs WHERE SQL, exploring their syntax, functionality, and best use cases.

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Review

1. Understanding WHERE Clause:

The WHERE clause is commonly used to filter rows based on specific conditions in a SELECT, UPDATE, DELETE, or INSERT statement. It is applied before any grouping or aggregation occurs and filters rows based on individual column values.

2. Understanding HAVING Clause:

Unlike the WHERE clause, which filters rows before grouping, the HAVING clause is applied after data has been grouped using the GROUP BY clause. It filters grouped rows based on aggregate functions or calculated values.

3. Syntax Comparison HAVING vs WHERE SQL:

WHERE Clause Syntax:

1. WHERE Clause Syntax:

SELECT column1, column2

FROM table_name

WHERE condition;

HAVING Clause Syntax:

2. HAVING Clause Syntax:

SELECT column1, aggregate_function(column2)

FROM table_name

GROUP BYcolumn1

HAVING condition;

4. Use Cases:

WHERE Clause Use Cases:
- Filtering individual rows based on specific criteria.
- Conditions involving non-aggregated column values.
- Used with SELECT, UPDATE, DELETE, or INSERT statements.
- Applied early in query execution, reducing the number of rows processed.
- Efficient for filtering individual rows based on indexed columns.
HAVING Clause Use Cases:
- Filtering grouped results based on aggregate values.
- Conditions involving aggregated column values.
- Used with GROUP BY clause to filter grouped data.
- Applied after data grouping, potentially processing larger result sets.
- May impact performance when filtering aggregated data.

5. Examples of HAVING vs WHERE SQL

Q. Suppose we want to select employees who belong to the Sales department and have a salary greater than $50,000.

SQL Code

Example of WHERE Clause:

SELECT *

FROM Employees

WHERE Department = 'Sales' AND Salary > 50000.00;

Q.Suppose we want to find departments where the average salary is greater than $50,000.

Example of HAVING Clause:

SELECT *Department, AVG(Salary) AS AverageSalary

FROM Employees

GROUP BY Department

HAVING AVG(Salary) > 50000.00;

In above these examples:

The WHERE clause filters rows based on individual column values before any aggregation.
The HAVING clause filters grouped rows based on aggregate functions like AVG() after the GROUP BY operation.