Postgres Pro
Downloads
Home   >   mailing lists

Thread: count & distinct

count & distinct

From
"Andrea Aime"
Date:
Hi people. I would like to make a query that
tells me how many distinct values there are
in a column. Standard count doesn't seems
to support a count distinct option.
select distint count(*) of course doens't
work (distinti clause is applied after the
result are calculated). I've tried to define
a view, but it didn't worked (
create view distValues as select distinct ...
but views doesn't support distinct clause)...

Well, maybe I should create a new aggregate
function, but before spending time on PGSQL
guide I would like to know if someone can
give me a fast tip... ;-)
Thanks in advance
Andrea

PS: well, of course I can open a cursor on
a "select distinct column from table" and then
loop over the cursor couting how many values
there are, but it seem a bit ugly...

RE: count & distinct

From
"Andrew Snow"
Date:
> Hi people. I would like to make a query that
> tells me how many distinct values there are
> in a column. Standard count doesn't seems
> to support a count distinct option.
> select distint count(*) of course doens't
> work (distinti clause is applied after the
> result are calculated). I've tried to define
> a view, but it didn't worked (
> create view distValues as select distinct ...
> but views doesn't support distinct clause)...


SELECT COUNT(DISTINCT field_name) FROM table_name;

Works for me in v7.


Regards,
Andrew Snow
als@fl.net.au

Re: count & distinct

From
Vashenko Maxim
Date:
Andrea Aime wrote:
>
> Hi people. I would like to make a query that
> tells me how many distinct values there are
> in a column. Standard count doesn't seems
> to support a count distinct option.
> select distint count(*) of course doens't
> work (distinti clause is applied after the
> result are calculated). I've tried to define
> a view, but it didn't worked (
> create view distValues as select distinct ...
> but views doesn't support distinct clause)...
>
> Well, maybe I should create a new aggregate
> function, but before spending time on PGSQL
> guide I would like to know if someone can
> give me a fast tip... ;-)
> Thanks in advance
> Andrea
>
> PS: well, of course I can open a cursor on
> a "select distinct column from table" and then
> loop over the cursor couting how many values
> there are, but it seem a bit ugly...


SELECT field, count(*) FROM table GROUP BY field



With best regards, Max Vaschenko,
Nizhny Novgorod Information Networks.