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Error related to only_full_group_by when executing a query in MySql

I have upgraded my system and have installed MySql 5.7.9 with php for a web application I am working on. I have a query that is dynamically created, and when run in older versions of MySQL it works fine. Since upgrading to 5.7 I get this error:

Expression #1 of SELECT list is not in GROUP BY clause and contains non-aggregated column 'support_desk.mod_users_groups.group_id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

Note the manual page for Mysql 5.7 on the topic of Server SQL Modes.

This is the query that is giving me trouble:

SELECT mod_users_groups.group_id AS 'value', 
       group_name AS 'text' 
FROM mod_users_groups
LEFT JOIN mod_users_data ON mod_users_groups.group_id = mod_users_data.group_id 
WHERE  mod_users_groups.active = 1 
  AND mod_users_groups.department_id = 1 
  AND mod_users_groups.manage_work_orders = 1 
  AND group_name != 'root' 
  AND group_name != 'superuser' 
GROUP BY group_name 
HAVING COUNT(`user_id`) > 0 
ORDER BY group_name

I don't understand only_full_group_by enough to figure out what I need to do to fix the query. Can I just turn off the only_full_group_by option, or is there something else I need to do?

Answer*

I would just add `group_id` to the `GROUP BY`. 

When `SELECT`ing a column that is not part of the `GROUP BY` there could be multiple values for that column within the groups, but there will only be space for a single value in the results. So, the database *usually* needs to be told exactly how to make those multiple values into one value. Commonly, this is done with an aggregate function like `COUNT()`, `SUM()`, `MAX()` etc... I say *usually* because most other popular database systems insist on this. However, in MySQL prior to version 5.7 the default behaviour has been more forgiving because it will not complain and then arbitrarily choose *any value*! It also has an `ANY_VALUE()` function that could be used as another solution to this question if you really needed the same behaviour as before. This flexibility comes at a cost because it is non-deterministic, so I would not recommend it unless you have a very good reason for needing it. MySQL are now turning on the `only_full_group_by` setting by default for good reasons, so it's best to get used to it and make your queries comply with it.

So why my simple answer above? I've made a couple of assumptions:

1) the `group_id` is unique. Seems reasonable, it is an 'ID' after all.

2) the `group_name` is also unique. This may not be such a reasonable assumption. If this is not the case and you have some duplicate `group_names` and you then follow my advice to add `group_id` to the `GROUP BY`, you may find that you now get more results than before because the groups with the same name will now have separate rows in the results. To me, this would be better than having these duplicate groups hidden because the database has quietly selected a value arbitrarily!    

It's also good practice to qualify all the columns with their table name or alias when there's more than one table involved... 



    SELECT 
      g.group_id AS 'value', 
      g.group_name AS 'text' 
    FROM mod_users_groups g
    LEFT JOIN mod_users_data d ON g.group_id = d.group_id 
    WHERE g.active = 1 
      AND g.department_id = 1 
      AND g.manage_work_orders = 1 
      AND g.group_name != 'root' 
      AND g.group_name != 'superuser' 
    GROUP BY 
      g.group_name, 
      g.group_id 
    HAVING COUNT(d.user_id) > 0 
    ORDER BY g.group_name

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2

In MySQL 5.7 they set a property that requires all non-aggregate fields in a query be a GROUP BY. So a query like SELECT a, SUM(b) FROM table; means that field "a" Must be in a GROUP BY. So if you don't have a GROUP BY then you must add it to the query. It is all about if you have at least one aggregate field in the SELECT portion of your query.

bytor99999
– bytor99999

2018-02-22 16:30:12 +00:00
Commented Feb 22, 2018 at 16:30

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Error related to only_full_group_by when executing a query in MySql

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