Source Code Examples

The COUNT function in MySQL is an aggregate function that returns the number of rows matching a specified condition. It's particularly useful when you need to know the number of records that match certain criteria.

Syntax

Here is the basic syntax for the COUNT function in MySQL:

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

In this syntax:

column_name: This is the name of the column for which you want to count the number of non-NULL values.

table_name: This is the name of the table from which you want to count.

condition: This is an optional part of the syntax. It specifies the condition that the rows must meet to be counted.

Demo Database

To demonstrate the examples, let's consider a demonstration database named SchoolDB with a table of Students. The Students table consists of the following columns: student_id, first_name, last_name, grade_level, major_subject.

Examples

Now, let's go through some practical examples of using the COUNT function:

Counting All Rows

To count all students in the Students table:

SELECT COUNT(*) FROM Students;

This command will return the total number of rows in the Students table.

Counting with a Condition

To count all students who are in grade_level 10:

SELECT COUNT(*) FROM Students WHERE grade_level = 10;

This will return the total number of students who are in the 10th grade.

Counting Distinct Values

To count the number of distinct major_subject among students:

SELECT COUNT(DISTINCT major_subject) FROM Students;

This will return the number of unique major subjects that the students have.

Summary

The COUNT function in MySQL is a powerful tool when you need to calculate the number of rows that match a specific condition. It's an essential part of SQL that can provide valuable insights into your data by offering a count of matching records.

By mastering the use of the COUNT function, you gain a potent instrument for quantitative database analysis. Whether you're calculating total records or determining the quantity of unique entries, the COUNT function provides the means to navigate your data more effectively.

MySQL