Обсуждение: Help ... Unexpected results when using limit/offset with select statement..DB corruption?

I got some weird results when processing select statements with limit and offset.   I think its some kind of database corruption but I was wondering what other’s think.

Background:

The table I’m having the issue with is described below.  The thing to note is the primary key 

ice=# \d nc_host_datum

        Table "public.nc_host_datum"

        Column        |  Type   | Modifiers

----------------------+---------+-----------

 host_id              | bigint  | not null

 host_datum_type_id   | integer | not null

 host_datum_source_id | integer | not null

 data                 | text    | not null

Indexes:

    "nc_host_datum_pkey" PRIMARY KEY, btree (host_id, host_datum_type_id)

Foreign-key constraints:

    "foreign_key_01" FOREIGN KEY (host_id) REFERENCES nc_host(host_id) ON UPDATE CASCADE ON DELETE CASCADE

    "foreign_key_02" FOREIGN KEY (host_datum_type_id) REFERENCES nc_host_datum_type(host_datum_type_id) ON UPDATE RESTRICT ON DELETE RESTRICT

    "foreign_key_03" FOREIGN KEY (host_datum_source_id) REFERENCES nc_host_datum_source(host_datum_source_id) ON UPDATE RESTRICT ON DELETE RESTRICT

Problem:

I perform the following select (notice that the group by is by the primary key). 

select host_id, host_datum_type_id, count(*)   

from nc_host_datum where host_id in

  ( select host_id 

  from nc_host 

  where audit_id=2041) 

group by host_id, host_datum_type_id;

and get the following result (There are many more rows but these are all the rows for host_id =   963711):

host_id   | host_datum_type_id | count 

-------------+------------------------------+---------

  963711 |                 58           |     1

  963711 |                 54           |     1

  963711 |                 39           |     1

  963711 |                 28           |     1

  963711 |                 27           |     1

Notice that there are 5 rows for host_id 963711 and the host_datum_type_id's are all unique 

Then I perform the following selects

SELECT host_id, host_datum_type_id, host_datum_source_id, data  

FROM nc_host_datum  INNER JOIN nc_host USING (host_id)  

WHERE audit_id=2041  

ORDER BY host_id  

LIMIT 49 OFFSET 1372;

And  

SELECT host_id, host_datum_type_id, host_datum_source_id, data  

FROM nc_host_datum  INNER JOIN nc_host USING (host_id)  

WHERE audit_id=2041  

ORDER BY host_id  

LIMIT 49 OFFSET 1421;

A portion of the output follows.  

 host_id | host_datum_type_id | host_datum_source_id |     data     

---------+--------------------+----------------------+--------------

  :

  :

  963710 |                 58 |                   17| harrish

  963711 |                 27 |                    3 | 1

  963711 |                 28 |                    3 | 1

(49 rows)

 host_id | host_datum_type_id | host_datum_source_id |     data     

---------+--------------------+----------------------+--------------

  963711 |                 28 |                    3 | 1

  963711 |                 58 |                   17 | lmitchel

  963711 |                 39 |                    3 | us.aegon.com 

:

: 

(49 rows)

Notice that host_id = 963711 and host_datum_type_id = 28 is repeated twice.  Since the offset is not overlapping, how can this happen?  Any ideas on how to fix this?

Thanks,

Barbara