Re: Distinct oddity

am 07.05.2009 20:54 Uhr schrieb Scott Marlowe unter scott(dot)marlowe(at)gmail(dot)com:

> On Thu, May 7, 2009 at 2:21 AM, Maximilian Tyrtania
> <maximilian(dot)tyrtania(at)onlinehome(dot)de> wrote:
>> Hi there,
>>
>> does this look right?
>>
>> FAKDB=# select count(distinct(f.land)) from firmen f where
>> f.typlist='Redaktion';
>>  count
>> -------
>>  1975
>> (1 row)
>>
>> FAKDB=# select count(distinct(f.land||'1')) from firmen f where
>> f.typlist='Redaktion';
>>  count
>> -------
>>  4944
>> (1 row)
>
> Yeah, that does seem odd. Could it be something like nulls in your
> data set? just guessing really. If you could make a small test case
> that shows it happening and allows others to reproduce it you're
> likely to get more bites.

It doesn't seem to be related to null values (which wouldn't explain it
anyway) nor to this particular field...

FAKDB=# select count(*) from firmen where bezeichnung is null;
count
-------
0
(1 row)

FAKDB=# select count(distinct(f.bezeichnung)) from firmen f;
count
-------
72698
(1 row)

FAKDB=# select count(distinct(f.bezeichnung||'e')) from firmen f;
count
-------
72892
(1 row)

My attempts at reproducing this with a freshly created table failed, of
course.

FAKDB=# create table concattest(mytext text);
CREATE TABLE
FAKDB=# insert into concattest (mytext)
select(generate_series(1,10000)::text);
INSERT 0 10000
FAKDB=# insert into concattest (mytext)
select(generate_series(1,10000)::text);
INSERT 0 10000
FAKDB=# select count(distinct(mytext)) from concattest;
count
-------
10000
(1 row)

FAKDB=# select count(distinct(mytext||'2')) from concattest;
count
-------
10000
(1 row)

best,

Maximilian Tyrtania