Postgres 15

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create table table_a (
  uuid int
);

insert into table_a values
(1),
(2);

create table table_b (
  uuid int
);

CREATE TABLE

INSERT 0 2

CREATE TABLE

with cte_table_a as (
  SELECT COUNT(DISTINCT uuid) AS entry_count_a FROM table_a
),
cte_table_b as (
  SELECT COUNT(DISTINCT uuid) AS entry_count_b FROM table_b
)
select * from cte_table_a
cross join cte_table_b

entry_count_a
entry_count_b

2
0

SELECT 1

SELECT * 
from (SELECT COUNT(DISTINCT uuid) AS entry_count_a FROM table_a) a
CROSS JOIN (SELECT COUNT(DISTINCT uuid) AS entry_count_b FROM table_b) b

entry_count_a
entry_count_b

2
0

SELECT 1