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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