COUNT

Counts the number of rows or not NULL values.

Syntax

COUNT([ DISTINCT ] <expr>)

COUNT(*) returns a total count of all rows in the table, while COUNT(<column_name>) returns a count of non-NULL rows in the specified <column_name>.

By default, COUNT(DISTINCT) returns approximate results. If you require a precise result (with a performance penalty), please contact Firebolt Support through the Help menu support form.

Example

For this example, we’ll create a new table number_test as shown below.

CREATE DIMENSION TABLE IF NOT EXISTS number_test
	(
		num TEXT
	);

INSERT INTO
	number_test
VALUES
	(1),
	(1),
	(2),
	(3),
	(3),
	(3),
	(4),
	(5);

Doing a regular COUNT returns the total number of rows in the column. We inserted 8 rows earlier, so it should return the same number.

SELECT
	COUNT(num)
FROM
	number_test;

Returns: 8

A COUNT(DISTINCT) function on the same column returns the number of unique rows. There are five unique numbers that we inserted earlier.

SELECT
	COUNT(DISTINCT num)
FROM
	number_test;

Returns: 5

To understand the difference between COUNT(DISTINCT pk) with exact precision enabled and using default approximation, consider a table, count_test with 8,388,608 unique pk values. The APPROX_COUNT_DISTINCT function returns the same approximate results as the COUNT(DISTINCT) function with exact precision disabled, so we can see the difference between these methods with the following example.

SELECT
	COUNT(DISTINCT pk) as count_distinct,
	APPROX_COUNT_DISTINCT(pk) as approx_count
FROM
	count_test;

Returns:

Assuming 8,388,608 unique pk values, we will see results like:

' +----------------+--------------+
' | count_distinct | approx_count |
' +----------------+--------------+
' |      8,388,608 |    8,427,387 |
' +----------------+--------------+