sql - 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 what I'm currently using (however I should be able to wrap it all up into a single SELECT statement):

SELECT "count"(*) AS val1 FROM tab1;
SELECT "count"(*) AS val2 FROM tab2;
SELECT val2-val1;

Thanks in advance

Answer 1

Try this way:

select 
  (
    SELECT 
      "count"(*) as val1 
    from 
      tab1
  ) - (
    SELECT 
      "count"(*) as val2 
    from 
      tab2
  ) as total_count