Question

I am trying to show a count for each age which is calculated from a Date of Birth column but the problem is it will only group by date of birth so there are a lot of duplicate ages being shown. Here is my query:

SELECT 
    DATEDIFF(hh, p.p_dob, GETDATE())/8766 AS Age,
    COUNT(DISTINCT s.s_studentreference) AS 'Count'    
FROM 
    moduleenrolment e
INNER JOIN 
    module m ON m.m_id = e.e_module
INNER JOIN 
    person p ON p.p_id = e.e_student
INNER JOIN 
    student s ON s.s_id = p.p_id
WHERE 
    m.m_reference LIKE '11%'
    AND LEN(m.m_reference) <= 12
    AND e.e_status IN ('A', 'W', 'C')
GROUP BY 
    p.p_dob
ORDER BY 
    p.p_dob DESC

This is a sample for the results

12  1
13  1
14  1
14  1
14  1
14  1
14  1
14  1
14  1
14  1
14  1

What I was looking for was

12 1
13 1
14 9

Answer 1

Group by and order by DATEDIFF(hh, p.p_dob, GETDATE())/8766 instead of p.p_dob

By grouping by p.p_dob, you’re effectively grouping by the unique date of birth instead of the calculated age.