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 

Answer 2

for same table you can do this.

select (count(abc)-count(DISTINCT xyz)) from tab;