在另一个查询中使用一个查询的结果

Question

I am very new to postgresql. I have a table which looks like this

NAME GPA SUBJECT
BEN 3.5 MATH
BEN 3.7 BIOLOGY
KATE 3.7 MATH
KATE 3.7 BIOLOGY

one query gives me the average gpa for everyone for all subjects.

select avg(gpa) from table;

result:

AVGALLGPA
3.8

another query gives the average gpa for each person.

select avg(gpa) from table group by name;

result:

NAME AVGGPA
BEN 3.78
KATE 3.83

now I am writing a query which counts how many students have avg better than overall avg.

select 
    count(case when avg(gpa)> avgallgpa then 1 
          else null end) 
from table;

how can I pass the result(the avgallgpa) from the previous query into the later query?

Answer 1

 select count(*) from (
    select name from the_table 
    group by name
    having avg(gpa) > (select avg(gpa) from the_table )
) t

Answer 2

You could use a Sub-query.

select COUNT(*) from table 
group by name having 
avg(gpa) > (select avg(gpa) from table);