Обсуждение: Novice SQL Question

I need to the following query:
select distinct event_code, level from logs join stat on (stat.prime is not
null) where order_num = 130680;

Ok, no problem. Does exactly what I want; however, I need to sort this is a
particular way to get the right results. When I try to add the order by
clause, I get an error. Here is the ORDER BY:
ORDER BY event_date DESC, event_time DESC, event_secs DESC

If I put this where I thought it should go as in:
select distinct event_code,level from logs join stat on (stat.prime is not
null) where order_num = 130680 order by event_date,event_time,event_secs;

I get the following error:
ERROR:  For SELECT DISTINCT, ORDER BY expressions must appear in target list

No matter where I put it I get errors. Obviously, I'm a novice. Can somebody
give me any advice? I'm using Postgres 7.2.3 on RedHat.

Thanks...
-- Work: 1-336-372-6812Cell: 1-336-363-4719
email: terry@esc1.com

To answer my own question:

I discoverd that the order by fields had to be in the select list. Apparently,
this is a requirement when using "DISTINCT".

On Monday 02 February 2004 05:38 pm, Terry Lee Tucker wrote:
> I need to the following query:
> select distinct event_code, level from logs join stat on (stat.prime is not
> null) where order_num = 130680;
>
> Ok, no problem. Does exactly what I want; however, I need to sort this is a
> particular way to get the right results. When I try to add the order by
> clause, I get an error. Here is the ORDER BY:
> ORDER BY event_date DESC, event_time DESC, event_secs DESC
>
> If I put this where I thought it should go as in:
> select distinct event_code,level from logs join stat on (stat.prime is not
> null) where order_num = 130680 order by event_date,event_time,event_secs;
>
> I get the following error:
> ERROR:  For SELECT DISTINCT, ORDER BY expressions must appear in target
> list
>
> No matter where I put it I get errors. Obviously, I'm a novice. Can
> somebody give me any advice? I'm using Postgres 7.2.3 on RedHat.
>
> Thanks...

--
Quote: 48
"Exceeding the bounds of authority is no more a right in a great thanin a petty officer, no more justifiable in a king
thanin a constable;but is so much the worse in him, in that he has more trust put in him,has already a much greater
sharethan the rest of his brethren, and issupposed from the advantages of his education, employment, and coun-sellors,
tobe more knowing in the measures of right and wrong." 
--John Locke
Work: 1-336-372-6812Cell: 1-336-363-4719
email: terry@esc1.com

Terry Lee Tucker <terry@esc1.com> writes:
> If I put this where I thought it should go as in:
> select distinct event_code,level from logs join stat on (stat.prime is not 
> null) where order_num = 130680 order by event_date,event_time,event_secs;

> I get the following error:
> ERROR:  For SELECT DISTINCT, ORDER BY expressions must appear in target list

Right.  Think about what SELECT DISTINCT does: it combines all rows with
the same values of event_code and level into a single row.  The group of
rows with a particular pair of event_code/level might contain many
different values of event_date etc.  Which of these values should be
used to sort the combined row?  The result just isn't well-defined in
general.  You need to alter the query so that it completely defines
the result you want.  One way to do that is suggested by the error
message: add the ORDER BY columns into the DISTINCT list.  But that's
not necessarily the way that will get the result you want.
        regards, tom lane