postgresql - sql - count of `true` values

Since PostgreSQL 9.4 there's the FILTER clause, which allows for a very concise query to count the true values:

select count(*) filter (where myCol)
from tbl;

The above query is a bad example in that a simple WHERE clause would suffice, and is for demonstrating the syntax only. Where the FILTER clause shines is that it is easy to combine with other aggregates:

select count(*), -- all
       count(myCol), -- non null
       count(*) filter (where myCol) -- true
from tbl;

The clause is especially handy for aggregates on a column that uses another column as the predicate, while allowing to fetch differently filtered aggregates in a single query:

select count(*),
       sum(otherCol) filter (where myCol)
from tbl;

SELECT COALESCE(sum(CASE WHEN myCol THEN 1 ELSE 0 END),0) FROM <table name>

or, as you found out for yourself:

SELECT count(CASE WHEN myCol THEN 1 END) FROM <table name>

Cast the Boolean to an integer and sum.

SELECT count(*),sum(myCol::int);

You get 6,3.