The Difference Between Order By and Group By in SQL
When it comes to SQL, understanding the difference between order by and group by can be crucial to writing efficient and effective queries. Although these two commands may sound similar, they serve distinct purposes.
Order By
The order by clause is used to sort the result set by one or more columns. This command is included after the from statement and before any group by clause.
For example, if you were to write a query to return a list of employees sorted alphabetically by last name, you would use the following code:
SELECT * FROM employees ORDER BY last_name ASC;
This query would result in a list of employees sorted in ascending order by their last name.
Another use of order by is to sort columns by multiple conditions. To do this, you would simply list the columns in the order you want them sorted, separated by commas.
For example, if you wanted to sort your employees first by department and then by last name, you would use the following code:
SELECT * FROM employees ORDER BY department DESC, last_name ASC;
This query would result in a list of employees sorted in descending order by their department, and then in ascending order by their last name.
Group By
The group by clause is used for aggregating data by one or more columns. This command is included after the from statement and where clause, but before any order by clause.
For example, if you were to write a query to return the average salary of employees by department, you would use the following code:
SELECT department, AVG(salary) FROM employees GROUP BY department;
This query would result in a list of departments and their average salary.
Another use of group by is to count the number of occurrences of a specific value. To do this, you would use the count function.
For example, if you wanted to count the number of employees in each department, you would use the following code:
SELECT department, COUNT(*) FROM employees GROUP BY department;
This query would result in a list of departments and their respective employee count.
Conclusion
In summary, the order by clause is used to sort the result set by one or more columns, while the group by clause is used for aggregating data by one or more columns. Understanding the difference between these two commands can help you write more efficient and effective query statements in SQL.
Table difference between order by and group by
| Order By | Group By |
|---|---|
| Orders the result set based on the specified column(s) | Groups the result set based on specified column(s) |
| Can be used with any select statement | Primarily used with aggregate functions (COUNT, SUM, AVG, etc.) |
| Sorts the rows in ascending or descending order | Combines rows with the same values in the specified column(s) into a single row |
| Does not affect the number of rows returned | Reduces the number of rows returned by combining values |
| Can be used with multiple columns to order the result set by multiple criteria | Can be used with multiple columns to group the result set by multiple criteria |