Count Distinct on multiple values within same column in SQL Aggregation

Question

Objective:

I wanted to show the number of distinct IDs for any combination selected.

In the below example, I have data at a granular level: ID level data.

I wanted to show the number of distinct IDs for each combination.

For this, I use count distinct which will give me '1' for the below combinations.

But let's say if I wanted to find the number of IDs who made both E-commerce and Face to face transactions, in that case, if I just use this data, I would be showing the sum of E-comm and Face to face and the result would be '2' instead of '1'.

And this is not limited to Ecom/Face to face. I wanted to apply the same logic for all columns.

Please let me know if you have any other alternative approach to address this issue.

Answer 1

First aggregate in your table to get the distinct id s for each TranType :

SELECT TranType, COUNT(DISTINCT id) counter_distinct
FROM tablename
GROUP BY TranType

and then join to the table:

SELECT t.*, g.counter_distinct
FROM tablename t 
INNER JOIN (
  SELECT TranType, COUNT(DISTINCT id) counter_distinct
  FROM tablename
  GROUP BY TranType
) g ON g.TranType = t.TranType

Or use a correlated subquery:

SELECT t1.*, 
       (SELECT COUNT(DISTINCT t2.id) FROM tablename t2 WHERE t2.TranType = t1.TranType) counter_distinct
FROM tablename t1

Answer 2

But let's say if I wanted to find the number of IDs who made both E-commerce and Face to face transactions, in

You can get the list of ids using:

select id
from t
where tran_type in ('Ecomm', 'Face to face')
group by id
having count(distinct tran_type) = 2;

You can get the count using a subquery:

select count(*)
from (select id
      from t
      where tran_type in ('Ecomm', 'Face to face')
      group by id
      having count(distinct tran_type) = 2
     ) i;