In MySQL, COUNT() function used to return the number of rows that matches with a specified criteria.

Syntax:

COUNT(column_name)

When we use COUNT(column_name) function in select query it returns the number of rows for the specified column:

SELECT COUNT(column_name) FROM table_name;

COUNT(*)

When we use COUNT(column_name) function in select query it returns the number of records in a table:

SELECT COUNT(*) FROM table_name;

COUNT(DISTINCT column_name)

When we use COUNT(DISTINCT column_name) function in select query it returns the number of rows(distinct values) of the specified column:

SELECT COUNT(DISTINCT column_name) FROM table_name;

Example:

We have a table "user" as below:

    user
    id  first_name            last_name       country
    .......................................................
    1   John                     Simp         Canada
    2   Chris                    Hely         Korea
    3   Joy                      Roy          Canada
    4   Jenny                    Mill         Canada

COUNT(column_name)

The below query counts the number of user where country is Canada from the "user" table:

SELECT COUNT(country) AS count FROM user
WHERE country="Canada";

Result

count
........
3

COUNT(*)

The below query counts the total number of users in the "user" table:

SELECT COUNT(*) AS totalUser FROM users;

Result

totalUser
........
4

COUNT(DISTINCT column_name) Example

The below query counts the number of unique users in the "user" table:

SELECT COUNT(DISTINCT country) AS count FROM Orders;

Result

count
........
2

Hope this will help you :)