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PostgreSQL – COUNT() Function

  • Last Updated : 01 Jun, 2020

The COUNT() function is an aggregate function that enables users to get the number of rows that match a particular requirement of a query.
Depending upon the user requirements the COUNT() function can have the following syntaxes:

Syntax: COUNT(*)
Returns: All rows including NULL and Duplicates

Syntax: COUNT(column)
Returns:  All rows except NULL.

Syntax: COUNT(DISTINCT column)
Returns: All rows without NULL and Duplicates

The COUNT() function is used with the SELECT statement.

For examples we will be using the sample database (ie, dvdrental).
Example 1:
In this example we will use the COUNT(*) function to get the number of transactions in the payment table using the command below:

SELECT
   COUNT(*)
FROM
   payment;

Output:

Example 2:
In this example we will query for the distinct amounts which customers paid, using the COUNT(DISTINCT column) function as shown below:



SELECT
    COUNT (DISTINCT amount)
FROM
    payment;

Output:

Example 3:
Here we will be using the COUNT() function to get the details of customers who have made more than 40 payments:

SELECT
    customer_id,
    COUNT (customer_id)
FROM
    payment
GROUP BY
    customer_id
HAVING
    COUNT (customer_id) > 40;

Output:

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