postgresql - sql - count of `true` values

myCol
------
 true
 true
 true
 false
 false
 null

In the above table, if I do :

select count(*), count(myCol);

I get 6, 5

I get 5 as it doesn't count the null entry.

How do I also count the number of true values (3 in the example)?

(This is a simplification and I'm actually using a much more complicated expression within the count function)

Edit summary: I also want to include a plain count(*) in the query, so can't use a where clause

Solution 1:

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>

Solution 2:

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;