The **`COUNT` function** returns the number of rows in a table. With this function, you can count all the rows that fulfill a specified condition.

`COUNT` has three forms: `COUNT(*)`, `COUNT(expression)`, and `COUNT(DISTINCT expression)`.

To visualize each function form, we will be using the data set `numbers` with the values below as an example.

# COUNT(*)

The **`COUNT(*)` function** returns the number of rows in a dataset using the `SELECT` statement. The function counts rows with NULL, duplicate, and non-NULL values.

You can also use the `WHERE` clause to specify a condition.

SELECT COUNT(*) 
FROM numbers
WHERE val = 5;

# COUNT(expression)

The `COUNT(expression)` function returns the number of rows that do not contain NULL values.


Row six contains a NULL val, so the expression will return $6$.

# COUNT(DISTINCT expression)

The `COUNT(DISTINCT expression)` function returns the number of *distinct* non-NULL values.



SELECT COUNT(DISTINCT val) 
FROM numbers;

Row $1$ and $2$ share the same value, row $3$ and $5$ share the same value and row $6$ has a NULL value, which leaves only $4$ distinct non-NULL rows.

How to use the COUNT function in MySQL

The COUNT function in MySQL counts rows with three forms: *, expression, and DISTINCT expression.