% of total calculation without subquery in Postgres

Question

I'm trying to create a "Percentage of Total" column and currently using a subquery with no issues:

SELECT ID, COUNT(*), COUNT(*) / (SELECT COUNT(*)
FROM DATA) AS % OF TOTAL FROM DATA GROUP BY ID;

|  ID  | COUNT | % OF TOTAL |
|  1   |  100  |    0.10    |
|  2   |  800  |    0.80    |
|  3   |  100  |    0.10    |

However, for reasons outside the scope of this question, I'm looking to see if there is any way to accomplish this without using a subquery. Essentially, the application uses logic outside of the SQL query to determine what the WHERE clause is and injects it into the query. That logic does not account for the existence of subqueries like the above, so before going back and rebuilding all of the existing logic to account for this scenario, I figured I'd see if there's another solution first.

I've tried accomplishing this effect with a window function, but to no avail.

Answer 1

Use window functions:

SELECT ID, COUNT(*),
       COUNT(*) / SUM(COUNT(*)) OVER () AS "% OF TOTAL"
FROM DATA
GROUP BY ID;