Calculate the difference between results of two count(*) queries based on 2 tables in PostgreSQL

Question

I want to calculate the difference between the results of 2 count(*)-type SELECT queries executed on 2 separate tables of my PostgreSQL database.

This w

Answer 1

Another option is to use SUM:

SELECT SUM(val) AS result
FROM (SELECT count(*) AS val FROM tab2
      UNION ALL
      SELECT -count(*) FROM tab1) sub;

db<>fiddle demo