Question

What I would like is to count the array elements which corresponds to true (attendance), false (non-attendance) and NULL for any single event.

EDIT:

I just realized that arrays do not behave as I thought in pSQL, so a simple

userconfirm bool[]

Might suffice. However, I am still having the same problem counting true/false/null values. I will attempt to edit the question below to match this new constraint. I apologize for any errors.

---

I have a column such as

userconfirm bool[]

Where userconfirm[314] = true would mean that user #314 will attend. (false = no attend, NULL = not read/etc).

I’m not sure this is the best solution for this functionality (users announce their attendance to an event), but I am having trouble with an aggregate function on this column.

select count(*) from foo where id = 6 AND true = ANY (userconfirm);

This only returns 1, and trying to google “counting arrays” does not turn up anything useful.

How would I go about counting the different values for a single event?

Answer 1

You can use unnest in your SELECT like this:

select whatever,
       (select sum(case b when 't' then 1 else 0 end) from unnest(userconfirm) as dt(b))
from your_table
-- ...

For example, given this:

=> select * from bools;
 id |     bits     
----+--------------
  1 | {t,t,f}
  2 | {t,f}
  3 | {f,f}
  4 | {t,t,t}
  5 | {f,t,t,NULL}

You’d get this:

=> select id, (select sum(case b when 't' then 1 else 0 end) from unnest(bits) as dt(b)) as trues from bools;
 id | trues 
----+-------
  1 |     2
  2 |     1
  3 |     0
  4 |     3
  5 |     2

If that’s too ugly, you could write a function:

create function count_trues_in(boolean[]) returns bigint as $$
    select sum(case b when 't' then 1 else 0 end)
    from unnest($1) as dt(b)
$$ language sql;

and use it to pretty up your query:

=> select id, count_trues_in(bits) as trues from bools;
 id | trues 
----+-------
  1 |     2
  2 |     1
  3 |     0
  4 |     3
  5 |     2