Re: Counting boolean values (how many true, how many false)

[Thom Brown <thom@xxxxxxxxx>]

On 16 November 2010 16:49, maarten <maarten.foque@xxxxxxxxx> wrote:
> Hi,
>
> sum doesn't like booleans, but it does like integers so:
> sum(boolval::int) solves that problem for you.
>
> SELECT id,sum(good::int + fair::int + nice::int) would get you a total
> of the three for each row
>
> good luck,
> Maarten

Or, if you want a more flexible solution, you could try this:

CREATE OR REPLACE FUNCTION countif_add(current_count int, expression bool)
RETURNS int AS
$BODY$
BEGIN
	IF expression = true THEN
		RETURN current_count + 1;
	ELSE
		RETURN current_count;
	END IF;
END;
$BODY$
LANGUAGE plpgsql

CREATE AGGREGATE countif (boolean)
(
    sfunc = countif_add,
    stype = int,
    initcond = 0
);

Then you can call:

SELECT countif(fair) AS 'total fair', countif(!fair)
AS 'total unfair'
FROM pref_rep;

But it also would let you do stuff like:

SELECT countif(my_column > 3) AS 'stuff greater than 3',
countif(this_column = that_column) AS 'balanced values' FROM my_table;

-- 
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935

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