Today I Learned

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Count true values with postgres

I can try to count everything that is not null in postgres:

select count(x.x)
from (
  values (null), ('hi'), (null), ('there')
) x (x);
# 2

But if I try to count everything that is true in postgres, I don’t get what I want:

select count(x.x)
from (
  values (false), (true), (false), (true)
) x (x);
# 4

I can, however, take advantage of the postgres ability to cast boolean to int:

select true::int;
# 1
select false::int;
# 0

Using ::int I get:

select count(x.x::int)
from (
  values (false), (true), (false), (true)
) x (x);
# 4

Postgres is still counting everything that is not null, but what if use sum instead?

select sum(x.x::int)
from (
  values (false), (true), (false), (true)
) x (x);
# 2

Because everything is either a 0 or a 1, sum behaves like count.

Now you can do something like this:

select
  sum((status = 'Awesome')::int) as awesomes,  
  sum((status = 'Terrible')::int) as terribles
from statuses;
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