[GENERAL] why isn't this subquery wrong?

CREATE TEMPORARY TABLE example_a__data (

foo_id INT,

bar_id INT

);

CREATE TEMPORARY TABLE example_a__rollup_source (

id int primary key,

name varchar(64),

foo_id INT,

check_bool BOOLEAN

);

CREATE TEMPORARY TABLE example_a__rollup AS

SELECT id, name, foo_id

FROM example_a__rollup_source

WHERE check_bool IS TRUE

;

SELECT foo_id

FROM example_a__data

WHERE foo_id IN (SELECT bar_id FROM example_a__rollup)

;