MAX() and MAX() OVER PARTITION BY produces error 3504 in Teradata Query

Question

I am trying to produce a results table with the last completed course date for each course code, as well as the last completed course code overall for each employee. Below is my query:

SELECT employee_number,
       MAX(course_completion_date) 
           OVER (PARTITION BY course_code) AS max_course_date,
       MAX(course_completion_date) AS max_date
FROM employee_course_completion
WHERE course_code IN ('M910303', 'M91301R', 'M91301P')
GROUP BY employee_number

This query produces the following error:

3504 : Selected non-aggregate values must be part of the associated group

If I remove the MAX() OVER (PARTITION BY...) line, the query executes just fine, so I've isolated the problem to that line, but after searching these forums and the internet I can't see what I'm doing wrong. Can anyone help?

Answer 1

Logically OLAP functions are calculated after GROUP BY/HAVING, so you can only access columns in GROUP BY or columns with an aggregate function. Following looks strange, but is Standard SQL:

SELECT employee_number,
       MAX(MAX(course_completion_date)) 
           OVER (PARTITION BY course_code) AS max_course_date,
       MAX(course_completion_date) AS max_date
FROM employee_course_completion
WHERE course_code IN ('M910303', 'M91301R', 'M91301P')
GROUP BY employee_number, course_code

And as Teradata allows re-using an alias this also works:

SELECT employee_number,
       MAX(max_date) 
           OVER (PARTITION BY course_code) AS max_course_date,
       MAX(course_completion_date) AS max_date
FROM employee_course_completion
WHERE course_code IN ('M910303', 'M91301R', 'M91301P')
GROUP BY employee_number, course_code