MySQL COUNT() Function
The COUNT() function returns the number of rows that matches a specified criterion.
COUNT() Syntax
SELECT COUNT([DISTINCT] column_name | *)
FROM table_name
WHERE condition;
The behavior of COUNT() depends on the argument used within the parentheses:
COUNT(*)- Counts the total number of rows in a table (including NULL values).COUNT(columnname)- Counts all non-null values in the column.COUNT(DISTINCT columnname)- Counts only the unique, non-null values in the column.
Demo Database
Below is a selection from the "Products" table in the Northwind sample database:
| ProductID | ProductName | SupplierID | CategoryID | Unit | Price |
|---|---|---|---|---|---|
| 1 | Chais | 1 | 1 | 10 boxes x 20 bags | 18.00 |
| 2 | Chang | 1 | 1 | 24 - 12 oz bottles | 19.00 |
| 3 | Aniseed Syrup | 1 | 2 | 12 - 550 ml bottles | 10.00 |
| 4 | Chef Anton's Cajun Seasoning | 2 | 2 | 48 - 6 oz jars | 22.00 |
| 5 | Chef Anton's Gumbo Mix | 2 | 2 | 36 boxes | 21.35 |
Using COUNT(*)
The following SQL uses COUNT(*), and counts the total number of rows in the "Products" table (will include NULL values):
Example
SELECT COUNT(*)
FROM Products;
Using COUNT(column_name)
The COUNT(column_name) counts all non-null values in the specified column.
The following SQL counts all non-null values of the "ProductName" column:
Example
SELECT COUNT(ProductID)
FROM Products;
Using COUNT(DISTINCT column_name)
You can ignore duplicates by using the DISTINCT keyword.
The COUNT(DISTINCT column_name) counts only the unique, non-null values in the column.
If DISTINCT is specified, rows with the same value for the specified column will be counted as one.
The following SQL counts the unique, non-null values of the "Price" column:
Example
SELECT COUNT(DISTINCT Price)
FROM Products;
Add a WHERE Clause
You can add a WHERE clause to specify conditions:
Example
SELECT COUNT(ProductID)
FROM Products
WHERE Price > 20;
