what is sql command for this group by?

Question

i have a table with this columns:"id,Nationalcode,Ccode,Ocode,Adate,..." now i want do group by on Nationalcode, select id,Kasset from allocate group by Kasset

but for each Nationalcode there are several record hence hit to following error: Column 'allocate.Id' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

what is correct command?

Answer 1

It's clear enough from the error message

Column 'allocate.Id' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause

that while having several Allocate.Id values, eg

1, 2, 3

you have to figure out one with a help of aggregate function :

1, 2, 3 -> SUM()   -> 6
1, 2, 3 -> AVG()   -> 2
1, 2, 3 -> MIN()   -> 1
1, 2, 3 -> MAX()   -> 3
1, 2, 3 -> COUNT() -> 3

etc. The query should be

    select Max(Id), --TODO: Put the right function here 
           Kasset 
      from Allocate 
  group by Kasset

Edit : let's try finding out these aggregate functions (at least some of them), according to the example (see comments below)

id | Nationalcode | Ccode | Ocode | Kasset |    Adat
-------------------------------------------------------
 1 |          547 |  1910 |     1 |   4444 | 1995/09/27
 2 |          546 |  1910 |     1 |   2222 | 1995/12/14
 1 |          546 |  1910 |     1 |   4444 | 1995/01/01

The desired result is

 1 |          546 |  1910 |     1 |   4444 | 1995/09/27
 2 |          546 |  1910 |     1 |   2222 | 1995/12/14

the query can be

    select Max(Id),           -- ? Many options, Max among them 
           Min(Nationalcode), -- since 546, 547 -> 546 
           Max(Ccode),        -- ? Many options, Max among them
           Max(Ocode),        -- ? Many options, Max among them
           Kasset,            -- ? Many options, Max among them
           Max(Adat)          -- 1995/09/27, 1995/01/01 -> 1995/09/27 
      from Allocate 
  group by Kasset

Answer 2

GROUP BY clause is always used with aggregate function (ie SUM, COUNT, MIN, MAX, or AVG functions)

Try this:

select count(id) [Count], Kasset from allocate group by Kasset