how can oracle SQL return 6 count(columns) from one

Question

I try to create a query, which counts different emission classes of cars, grouped by different country codes.

I can handle to do it with one emission_class , but fail to create it with all 7 of them. I'm not sure how to start a subquery for this, or should I try to UNION them?

thank you for your insight!

The code for a singel emission class count:

SELECT
  DISTINCT country_code,
  COUNT(emission_class) EURO0
FROM
  DB.CUSTOMER_VEHICLE
WHERE emission_class = 'E0'
GROUP BY country_code;

Answer 1

You can use SUM with CASE :

SELECT country_code
     , COUNT(emission_class) AS total
     , SUM(CASE WHEN emission_class = 'E0' THEN 1 ELSE 0 END) AS EURO0
     , SUM(CASE WHEN emission_class = 'E?' THEN 1 ELSE 0 END) AS EURO?
     , ...
FROM DB.CUSTOMER_VEHICLE
GROUP BY country_code;

Answer 2

This is what I think @Nightmaresux was trying to suggest:

SELECT country_code,
       emission_class,
       COUNT(*) cnt
FROM   DB.CUSTOMER_VEHICLE
GROUP BY country_code, emission_class;

It's an alternative to @notulysses's answer, but is slightly more flexible since it will work for any emission_class. However, it won't put each count into a new column, so it depends on what you're wanting the output to look like as to which proposed solution you go with.