Question

I should note that id is not unique in the tdemog_pfp table – there is a unique field there that auto-increments – could this be an issue?

Ok, I have the following SQL query:

SELECT id, name, total_staff AS StaffCount, COUNT( q60a ) AS TotalResp, (COUNT( q60a ) / total_staff * 100) AS Perc 
FROM tdemog_pfp
LEFT JOIN tresults_pfp ON tdemog_pfp.id = tresults_pfp.q60a
GROUP BY name
ORDER BY name

Now, the demog table has multiple rows where entries can have q59, q60a, q60b and so on for the colomn qnum

I want to bring back the results WHERE qnum = q60a but I have a problem, when I add it to the above to make the following – it brings back zero results (an empty result set), which is incorrect:

SELECT id, name, total_staff AS StaffCount, COUNT( q60a ) AS TotalResp, (COUNT( q60a ) / total_staff * 100) AS Perc 
FROM tdemog_pfp
LEFT JOIN tresults_pfp ON tdemog_pfp.id = tresults_pfp.q60a
    WHERE qnum = q60a
GROUP BY name
ORDER BY name

Where am I going wrong?

Thanks,

H.

Answer 1

Make your test part of the JOIN condition instead of testing in the WHERE clause.

SELECT id, name, total_staff AS StaffCount, COUNT( q60a ) AS TotalResp, (COUNT( q60a ) / total_staff * 100) AS Perc 
FROM tdemog_pfp
LEFT JOIN tresults_pfp ON tdemog_pfp.id = tresults_pfp.q60a
    AND qnum = q60a
GROUP BY name
ORDER BY name