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Editorial Team
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Asked: 2026-05-16T06:25:10+00:00

I am trying to pull multiple columns from 3 joined tables, but I want

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I am trying to pull multiple columns from 3 joined tables, but I want the result set to contain only one distinct “data entry” per p.id (the pet id which is a foreign key in the data entry table). The issue i have is that there could be two data entries, numbered 1 and 2, belonging to a pet – the query has to just pick the data entry with the highest number – that’s why i was trying to use max and group by but it doesn’t quite work. Can anyone see where i’m going wrong? Many thanks

SELECT `p`.`id`, `o`.`id`, `o`.`email`, MAX(d.number), `d`.`number`
FROM (`pets` AS `p`, `owners` AS `o`, `data_entries` AS `d`) 
WHERE `p`.`owner_id` = `o`.`id` 
AND `p`.`id` = `d`.`pet_id` 
GROUP BY `p`.`id` 
ORDER BY `d`.`number` DESC

EDIT: following iniju’s suggestion, I tried the following query, but this doesn’t not filter out the data entries where the number is lower than another data entry for the same pet :

SELECT `p`.`id`, `o`.`id`, `o`.`email`, `d`.`number`
FROM (`pets` AS `p`, `owners` AS `o`, `data_entries` AS `d`) 
WHERE `p`.`owner_id` = `o`.`id` 
AND `p`.`id` = `d`.`pet_id` 
GROUP BY `p`.`id`, `o`.`id`, `o`.`email`, `d`.`number`
HAVING `d`.`number`=MAX(`d`.`number`)
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1 Answer

  1. Editorial Team

    Your GROUP BY should contain all the non-aggregated columns that is:
    GROUP BY ‘p’.’id’, ‘o’.’id’, ‘o’.’email’, ‘d’.’number’

    Full query: 

    SELECT `p`.`id`, `o`.`id`, `o`.`email`, MAX(d.number)  
FROM (`pets` AS `p`, `owners` AS `o`, `data_entries` AS `d`)  
WHERE `p`.`owner_id` = `o`.`id`  
    AND `p`.`id` = `d`.`pet_id`  
GROUP BY `p`.`id`, `o`.`id`, `o`.`email`  
ORDER BY `d`.`number` DESC
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