Getting max,sum,count... funciton results for columns in form of a table

Question

Let's assume we have a table below having many rows and 4 columns A,B,C, D

+---+----+---+---+
| A |  B | C | D |
+---+--------+---+
| 1 | 1 | 1 |  2 |
| 2 | 2 | 2 |  2 |
| 3 | 3 | 3 |  2 |
| . | . | . |  . |
| . | . | . |  . |
+---+---+---+----+

Now I want the result in the form of a table like below using sql

+---------------+----------------+----------------+------------------+
|       A       |        B       |       C        |         D        |
+---------------+----------------+----------------+------------------+
| max(columnA)  | max(columnB)   | max(column C)  |  max(Column D)   |
| count(columnA)| count(columnB) | count(column C)|  count(Column D) |
| sum(columnA)  | sum(columnB)   | sum(column C)  |  sum(Column D)   |
+---------------+----------------+----------------+------------------+

I know this can be done using something shown below but is there a different way of doing it? The table I'm working on is a bit large and there are multiple functions which I would have to apply on it therefore the select query would be big and there would be multiple union statements, so is there a way to avoid it using 'union' method? Thank you for your help.

select max(A),max(b), max(c),max(d) from table where ...
UNion
select count(A),count(B),count(c),count(d) from table where ...
union
.
.

Answer 1

Use a CTE:

with summary as (
    select
        max(a) max_a,
        max(b) max_b,
        max(c) max_c,
        max(d) max_d,
        count(a) count_a,
        count(b) count_b,
        count(c) count_c,
        count(d) count_d,
        sum(a) sum_a,
        sum(b) sum_b,
        sum(c) sum_c,
        sum(d) sum_d
    from mytable
    -- optional joins, where clause, etc
)
select max_a a, max_b b, max_c c, max_d d from summary
union all
select count_a, count_b, count_c, count_d from summary
union all
select sum_a, sum_b, sum_c, sum_d from summary

Note the use of union all, which preserves duplicate rows, rather than union, which removes duplicates (although duplicates would be very unlikely here).