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Showing results as a percentage

With a table with data like this:

How can I show these results as a percentage (i.e count a / total records):
a 50
b 33.333
c 16.666
I know a GROUP BY must be there. I want to do this in one query.

I'll try to reproduce your scenario. Here's the SQL to create and populate the table:

create table MyTable
( MyColumn char(1) );

insert into MyTable values ('a');
insert into MyTable values ('a');
insert into MyTable values ('a');
insert into MyTable values ('b');
insert into MyTable values ('b');
insert into MyTable values ('c');
I came up with two different yet similar solutions. The first involves using a scalar subquery in the SELECT clause to obtain the total count. Here's the SQL:
select MyColumn, round( 100.0 * count(*) / 
                          ( select count(*)
                              from MyTable )
                        ,3 ) Perc
  from MyTable
  group by MyColumn;
The second solution involves a cross join with the same subquery. Because cross joins are the SQL equivalent to multiplication, and we know that the subquery returns one and only one row, then we know that the cross join will return one row per row in MyTable. Mathematically, this is the equivalent of saying, "X multiplied by 1 equals X." Grouping by T.CNT is required in order to make the join work, but this doesn't change the outcome because we know that T.CNT is constant for the entire query. And we know that having a secondary sort by a constant won't affect order.
select MyColumn, round(100.0 * count(*) / t.cnt,3) Perc
  from MyTable
       cross join
       ( select count(*) cnt from MyTable ) t
  group by MyColumn, t.cnt;
Both queries give the same result set:
-------- ----------
a                50
b            33.333
c            16.667
Which query you choose to use might depend on your particular SQL vendor's implementation, performance and/or which one you like better.

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