Column ‘Comments.Text’ is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause

aggregateazure-sql-databasegroup by

This question: Reason for Column is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause | Stack Overflow have explained the root of the problem very well and even advised to use max aggregate as a solution. But, lets take the example

group_id    item_id     comment
--------------------------------
1       abc     "blah-blah"
1       def     "tral-la-lah"
1       ghi
2       jkl
2       mno
2       pqr

I understand the solution: I must take an item to represent the group by max(item_id). But how do I take the comment of the selected item? How does it help me to take the corresponding comment?

edit

Everything is like in this question: Reason for Column is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause | Stack Overflow. The only complication that I address here is the extra comment column that I want to select along with the max(item_id) group by group_id.

I am using this beast, Which tools and technologies are used to build Data Explorer? | Meta Stack Exchange

Best Answer

Your question isn't really clear, but I think you want something like this:

select group_id, 
       item_id, 
       comment
from (
   select group_id,
          item_id, 
          comment, 
          row_number() over (partition by group_id order by item_id) as rn
   from the_unknown_table
) t
where rn = 1;

(you didn't state your DBMS, so this is ANSI SQL)

SQL Fiddle demo: http://sqlfiddle.com/#!12/a8471/1

Related Solutions

Postgresql – Error “column does not exist” in a SELECT with JOIN and GROUP BY query

You probably want something like this:

SELECT h_v_charges.*, 
       last_v.last_version
FROM hist_versions_charges h_v_charges 
  JOIN (select proj_charge_id, 
               max(version) as last_version
        from hist_versions_charges 
        where proj_sous_projet_id = 2  
        group by proj_charge_id
  ) last_v  
  ON h_v_charges.version = last_v.last_version
 AND h_v_charges.proj_charge_id = last_v.proj_charge_id 
ORDER BY h_v_charges.proj_charge_id ASC;

A possibly (because no join is required) faster solution would be:

select *
from (
   select hvc.*, 
          row_number() over (partition by proj_charge_id order by version desc) as rn
   from hist_versions_charges as hvc
   where proj_sous_projet_id = 2  
) as hv
where rn = 1
order by hv.proj_charge_id ASC;

As Colin has pointed out, this can also be written as:

with hv as (
  select hvc.*, 
         row_number() over (partition by proj_charge_id order by version desc) as rn
  from hist_versions_charges as hvc
  where proj_sous_projet_id = 2  
) 
select *
from hv
where rn = 1
order by hv.proj_charge_id ASC;

Mysql – group by clause without aggregate function

This:

SELECT users.* FROM users
INNER JOIN timesheets ON timesheets.user_id = users.id
WHERE (timesheets.submitted_at <= '2010-07-06 15:27:05.117700')
GROUP BY users.id

Finds all users who have a timesheet submitted on or before the given date. It's equivalent to:

SELECT DISTINCT users.* FROM users
INNER JOIN timesheets ON timesheets.user_id = users.id
WHERE (timesheets.submitted_at <= '2010-07-06 15:27:05.117700');

or:

SELECT  users.*
FROM users
WHERE EXISTS (
    SELECT 1
    FROM timesheets 
    WHERE timesheets.user_id = users.id
    AND timesheets.submitted_at <= '2010-07-06 15:27:05.117700'
);

It works because users.id is the primary key, so all other fields of users are functionally dependent on it. PostgreSQL knows that you don't have to use an aggregate to guarantee a single unambiguous result for each field in a row because there can only be one candidate users.name or whatever for any given users.id row.

(Older PostgreSQL versions didn't know how to identify functional dependencies of the primary key and and would throw an ERROR about needing to use an aggregate or include the field in the GROUP BY here).

Best Answer

Related Solutions

Postgresql – Error “column does not exist” in a SELECT with JOIN and GROUP BY query

Mysql – group by clause without aggregate function

Related Question