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Home Database Mysql Tutorial SQL Filtering and Sorting with Real Life Examples

SQL Filtering and Sorting with Real Life Examples

Apr 08, 2025 pm 06:15 PM

SQL Filtering and Sorting with Real Life Examples

This article will provide an in-depth explanation of WHERE , HAVING , ORDER BY , GROUP BY and other clauses and related operators in SQL through employee and department table cases, helping you master SQL data filtering and sorting skills.

Table of contents

  1. Table structure
  2. WHERE clause
  3. GROUP BY clause
  4. HAVING clause
  5. ORDER BY clause
  6. LIMIT clause
  7. DISTINCT clause
  8. AND , OR , NOT operators

Table structure

Employee List

emp_id name age department_id hire_date Salary
1 john smith 35 101 2020-01-01 5000
2 jane doe 28 102 2019-03-15 6000
3 alice johnson 40 103 2018-06-20 7000
4 bob brown 55 null 2015-11-10 8000
5 charlie black 30 102 2021-02-01 5500

Department list

dept_id Dept_name
101 hr
102 it
103 finance
104 Marketing

WHERE clause

The WHERE clause is used to filter records that meet certain criteria.

SQL Query:

 <code class="sql">SELECT name, age, salary FROM employees WHERE age > 30;</code>

result:

name age Salary
john smith 35 5000
alice johnson 40 7000
bob brown 55 8000

Description: Filter out information of employees older than 30 years old.

Example of AND operator:

 <code class="sql">SELECT name, age, salary FROM employees WHERE age > 30 AND salary > 5000;</code>

result:

name age Salary
alice johnson 40 7000
bob brown 55 8000

Description: Filter information of employees older than 30 years old and salary greater than 5,000.

GROUP BY clause

GROUP BY clause is used to group records with the same value and is often used in statistical aggregation operations.

SQL Query:

 <code class="sql">SELECT department_id, COUNT(*) AS employee_count FROM employees GROUP BY department_id;</code>

result:

department_id Employee_count
101 1
102 2
103 1

Description: Grouped by department ID and count the number of employees in each department.

HAVING clause

The HAVING clause is used to filter the results after GROUP BY grouping.

SQL Query:

 <code class="sql">SELECT department_id, AVG(salary) AS avg_salary FROM employees GROUP BY department_id HAVING AVG(salary) > 5500;</code>

result:

department_id avg_salary
102 5750
103 7000

Description: Filter out departments with an average salary of more than 5,500.

ORDER BY clause

ORDER BY clause is used to sort the result set.

SQL query (ascending order):

 <code class="sql">SELECT name, salary FROM employees ORDER BY salary;</code>

result:

name Salary
john smith 5000
charlie black 5500
jane doe 6000
alice johnson 7000
bob brown 8000

SQL query (descending order):

 <code class="sql">SELECT name, salary FROM employees ORDER BY salary DESC;</code>

result:

name Salary
bob brown 8000
alice johnson 7000
jane doe 6000
charlie black 5500
john smith 5000

LIMIT clause

The LIMIT clause is used to limit the number of records returned.

SQL Query:

 <code class="sql">SELECT name, salary FROM employees ORDER BY salary DESC LIMIT 3;</code>

result:

name Salary
bob brown 8000
alice johnson 7000
jane doe 6000

Description: Only the information of the top 3 employees is returned.

DISTINCT clause

The DISTINCT clause is used to remove duplicate values.

SQL Query:

 <code class="sql">SELECT DISTINCT department_id FROM employees;</code>

result:

department_id
101
102
103

Description: Returns the unique department ID.

AND , OR , NOT operators

These operators are used to combine multiple conditions.

(Omit repeated And, Or, Not examples, keep the space simple)

in conclusion

Through actual cases, this article explains in detail the key clauses and operators used in SQL for data filtering and sorting. Proficient in this knowledge will effectively improve your SQL query efficiency and data analysis capabilities.

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