SELECT COUNT(DISTINCT… ) error on multiple columns?

Question

I have a table, VehicleModelYear, containing columns id, year, make, and model.

The following two queries work as expected:

SELECT DISTINCT make, model
F         


        

Answer 1

The syntax is valid SQL but has not been implemented in SQL-Server.

Try a rewrite:

; WITH cte AS
  ( SELECT DISTINCT make, model
    FROM VehicleModelYear
  )
SELECT COUNT(*) AS total
FROM cte ; 

or:

; WITH cte AS
  ( SELECT COUNT(DISTINCT model) AS cnt
    FROM VehicleModelYear
    GROUP BY make
  )
SELECT SUM(cnt) AS total
FROM cte ; 

or:

; WITH cte AS
  ( SELECT NULL AS n
    FROM VehicleModelYear
    GROUP BY make, model
  )
SELECT COUNT(*) AS total
FROM cte ; 

And finally, the 2nd and 3rd query above modified, without subqueries:

SELECT DISTINCT
    SUM(COUNT(DISTINCT model)) OVER () AS total
FROM VehicleModelYear
GROUP BY make ;

SELECT DISTINCT COUNT(*) OVER () AS total
FROM VehicleModelYear
GROUP BY make, model ;

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Late additions by @Alexander Fedorenko:

SELECT TOP (1)
    SUM(COUNT(DISTINCT model)) OVER () AS total
FROM VehicleModelYear
GROUP BY make ;

SELECT TOP (1) COUNT(*) OVER () AS total
FROM VehicleModelYear
GROUP BY make, model ;

or:

; WITH cte AS
  ( SELECT DENSE_RANK() OVER(ORDER BY make, model) AS dr
    FROM VehicleModelYear
  )
SELECT MAX(dr) AS total
FROM cte ;

Answer 2

Try combining them into a single field:

SELECT COUNT(DISTINCT make + ' ' + model)
FROM VehicleModelYear

Answer 3

COUNT() in SQL Server accepts the following syntax

COUNT(*)
COUNT(colName)
COUNT(DISTINCT colName)

You can have a subquery which returns unique set of make and model that you can count with.

SELECT  COUNT(*)
FROM
        (
            SELECT  DISTINCT make, model
            FROM    VehicleModelYear
        ) a

The "a" at the end is not a typo. It's an alias without which SQL will give an error ERROR 1248 (42000): Every derived table must have its own alias.