COUNT() in PostgreSQL

The COUNT() function in PostgreSQL is used to count the number of rows in a table based on a given condition.

Syntax

SELECT COUNT(column_name) FROM table_name WHERE condition;

1. Counting All Rows in a Table

SELECT COUNT(*) FROM employees;

✅ Counts all rows in the employees table, including NULL values.

2. Counting Non-NULL Values in a Column

SELECT COUNT(salary) FROM employees;

✅ Counts rows where salary is not NULL.

3. Counting Rows with a Condition

SELECT COUNT(*) FROM employees WHERE department = 'IT';

✅ Counts employees only in the IT department.

4. Counting Unique Values (Using DISTINCT)

SELECT COUNT(DISTINCT department) FROM employees;

✅ Counts unique departments in the employees table.

5. Using GROUP BY with COUNT()

SELECT department, COUNT(*) FROM employees GROUP BY department;

✅ Counts employees in each department.

6. Using HAVING to Filter Groups

SELECT department, COUNT(*) FROM employees GROUP BY departmentHAVING COUNT(*) > 10;

✅ Retrieves only departments with more than 10 employees.