Is SQL GROUP BY a design flaw? [closed]

Answer 1

I agree its verbose that the group by list shouldn't implicitly be the same as then non-aggregated select columns. In Sas there are data aggregation operations that are more succinct.

Also : it's hard to come up with an example where it would be useful to have a longer list of columns in the group list than the select list. The best I can come up with is ...

create table people
(  Nam char(10)
  ,Adr char(10)
)

insert into people values ('Peter', 'Tibet')
insert into people values ('Peter', 'OZ')
insert into people values ('Peter', 'OZ')

insert into people values ('Joe', 'NY')
insert into people values ('Joe', 'Texas')
insert into people values ('Joe', 'France')

-- Give me people where there is a duplicate address record

select * from people where nam in 
(
select nam              
from People        
group by nam, adr        -- group list different from select list
having count(*) > 1
)

Answer 2

This thread provides some useful explanations.

http://social.msdn.microsoft.com/Forums/en/transactsql/thread/52482614-bfc8-47db-b1b6-deec7363bd1a

Answer 3

You don't have to group by the exactly the same thing you're selecting, e.g. :

SQL:select priority,count(*) from rule_class
group by priority


PRIORITY   COUNT(*)
      70          1
      50          4
      30          1
      90          2
      10          4

SQL:select decode(priority,50,'Norm','Odd'),count(*) from rule_class
group by priority

DECO   COUNT(*)
Odd           1
Norm          4
Odd           1
Odd           2
Odd           4

SQL:select decode(priority,50,'Norm','Odd'),count(*) from rule_class
group by decode(priority,50,'Norm','Odd')

DECO   COUNT(*)
Norm          4
Odd           8

Answer 4

I would say if you have a large number of items in the group by clause then perhaps the core info should be pulled out into a tabular sub-query which you inner join into.

There is a probably a performance hit, but it makes for neater code.

select  id, count(a), b, c, d
from    table
group by
        id, b, c, d

becomes

select  id, myCount, b, c, d
from    table t
        inner join (
            select id, count(*) as myCount
            from table
            group by id
        ) as myCountTable on myCountTable.id = t.id

That said, I'm interested to hear counter-arguments for doing this as opposed to having a large group by clause.

Answer 5

If you issue just regarding to easier way to write scripts. Here is one tip:

In MS SQL MGMS write you query in text something like select * from my_table after that select text right click and "Design Query in Editor.." Sql studio will open new editor with filed up all fields after that again right click and select "Add Gruop BY" Sql MGM studio will add code for you .

I fund this method extremely useful for insert statements. When I need to write script for insert a lot of fields in table, I just do select * from table_where_want_to_insert and after that change type of select statement to insert,

Answer 6

I Agree

I quite agree with the question. I asked the same one here.

I honestly think it's a language flaw.

I realise that there are arguments against that, but I have yet to use a GROUP BY clause containing anything other than all the non-aggregated fields from the SELECT clause in the real world.