COUNT

Counts the number of rows or not NULL values.

Syntax

COUNT([ DISTINCT ] <expr>)

Parameter	Description
`<expr>`	Valid values for the expression include column names (or * for counting all columns) or functions that return a column name. When `DISTINCT` is being used, counts only the unique number of rows with no `NULL` values.

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. To get a precise result, with a performance penalty, use SET firebolt_optimization_enable_exact_count_distinct=1;

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