MySQL COUNT – Counting Rows in a Table

Summary: in this tutorial, you will learn how to use the MySQL COUNT() function to return the number rows in a table.

Introduction to the MySQL COUNT() function

The COUNT() function is an aggregate function that returns the number of rows in a table. The COUNT() function allows you to count all rows or only rows that match a specified condition.

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

COUNT(*) function

The COUNT(*) function returns the number of rows in a result set returned by a SELECT statement. The COUNT(*) returns the number of rows including duplicate, non-NULL and NULL rows.

COUNT(expression)

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

COUNT(DISTINCT expression)

The COUNT(DISTINCT expression) returns the number of distinct rows that do not contain NULL values as the result of the expression.

The return type of the COUNT() function is BIGINT. The COUNT()  function returns 0 if there is no matching row found.

MySQL COUNT() function illustration

Setting up a sample table

First, create a table called count_demos:

CREATE
 
TABLE
 count_demos (    
id
 
INT
 AUTO_INCREMENT PRIMARY 
KEY
,    val 
INT
);
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

Second, insert some rows into the count_demos table:

INSERT
 
INTO
 count_demos(val) 
VALUES
(
1
),(
1
),(
2
),(
2
),(
NULL
),(
3
),(
4
),(
NULL
),(
5
);
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

Third, query data from the count_demos table:

SELECT
 * 
FROM
 count_demos;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

MySQL COUNT(*) example

The following statement uses the COUNT(*) function to return all rows from the count_demos table:

SELECT
 
COUNT
(*) 
FROM
 count_demos;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

This example uses the COUNT(*) function with a WHERE clause to specify a condition to count only rows whose value in the column  val is 2:

SELECT
 
COUNT
(*) 
FROM
 count_demos
WHERE
 val = 
2
;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

MySQL COUNT(expression) example

If you specify the val column in the COUNT() function, the COUNT() function will count only rows with non-NULL values in the  val column:

SELECT
 
COUNT
(val) 
FROM
 count_demos;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

Notice that two NULL values are not included in the result.

MySQL COUNT(DISTINCT expression) example

This example uses COUNT(DISTINCT expression) to count non-NULL and distinct values in the column val:

SELECT
 
COUNT
(
DISTINCT
 val)
FROM
 count_demos;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

MySQL COUNT() function practical examples

We’ll use the products table from the sample database for the next examples:

A) Using MySQL COUNT(*) function with a GROUP BY example

The COUNT(*) function is often used with a GROUP BY clause to return the number of elements in each group.

For example, this statement uses the COUNT() function with the GROUP BY clause to return the number of products in each product line:

SELECT
     productLine,     
COUNT
(*)
FROM
    products
GROUP
 
BY
 productLine;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

Similarly, this example uses the COUNT(*) function to find the number of products supplied by each vendor:

SELECT
     productVendor,     
COUNT
(*)
FROM
    products
GROUP
 
BY
 productVendor
ORDER
 
BY
 
COUNT
(*) 
DESC
;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

B) Using MySQL COUNT(*) with a HAVING clause example

To find vendors who supply at least 9 products, you use the COUNT(*) function in the HAVING clause as shown in the following query:

SELECT
     productVendor,     
COUNT
(*)
FROM
    products
GROUP
 
BY
 productVendor
HAVING
 
COUNT
(*) >= 
9
ORDER
 
BY
 
COUNT
(*) 
DESC
;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

C) MySQL COUNT IF example

You can use a control flow expression and functions e.g., IF, IFNULL, and CASE in the COUNT() function to count rows whose values match a condition.

See the following orders table from the sample database:

The following query use COUNT() with IF function to find the number of canceled, on hold and disputed orders from the orders table:

SELECT
     
COUNT
(
IF
(
status
 = 
'Cancelled'
, 
1
, 
NULL
)) 
'Cancelled'
,    
COUNT
(
IF
(
status
 = 
'On Hold'
, 
1
, 
NULL
)) 
'On Hold'
,    
COUNT
(
IF
(
status
 = 
'Disputed'
, 
1
, 
NULL
)) 
'Disputed'
FROM
    orders;
Code language:
 
SQL (Structured Query Language)
 
(
sql
)

Try It Out

The IF() function returns 1 if the order’s status is canceled, on hold or disputed, otherwise, it returns NULL.

The COUNT function only counts 1, not NULL values, therefore, the query returns the number of orders based on the corresponding status.

In this tutorial, you have learned various techniques to count the number of rows in a table using the MySQL COUNT function.

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