Rounding problems

Hi,

I have a problem with a query wich simple aggregate values. In the sample
below I have two values, 1.3 and 1.4. Rounding their average with one
decimals, should give 1.4.

The first query with - cast( tables_seb.tbl_arvier_chamencon.id_1 AS
numeric) AS value - give the expected result, while the second one with -
tables_seb.tbl_arvier_chamencon.id_1 AS value - give 1.3.

Which could be the reason ??

-- data

fulldate timestamp; tables_seb.tbl_arvier_chamencon.id_1- reals

2009-03-29 00:00:00; 1.3

2009-03-29 00:30:00; 1.4

--Good query

SELECT date_trunc('hour', data) AS data, round(cast(avg(value) AS numeric),
1 ) AS value

FROM

(

SELECT _master_30.fulldate AS data,

cast( tables_seb.tbl_arvier_chamencon.id_1 AS numeric) AS
value

--tables_seb.tbl_arvier_chamencon.id_1 AS value

FROM _master_30

LEFT JOIN tables_seb.tbl_arvier_chamencon ON
_master_30.fulldate = tables_seb.tbl_arvier_chamencon.fulldate

WHERE _master_30.fulldate between '2009-03-29 00:00:00' AND
'2009-03-29 00:59:59'

ORDER BY data

) foo

GROUP BY 1 ORDER BY 1;

-- value = 1.4 OK

--wrong query

SELECT date_trunc('hour', data) AS data, round(cast(avg(value) AS numeric),
1 ) AS value

FROM

(

SELECT _master_30.fulldate AS data,

--cast( tables_seb.tbl_arvier_chamencon.id_1 AS numeric) AS
value

tables_seb.tbl_arvier_chamencon.id_1 AS value

FROM _master_30

LEFT JOIN tables_seb.tbl_arvier_chamencon ON
_master_30.fulldate = tables_seb.tbl_arvier_chamencon.fulldate

WHERE _master_30.fulldate between '2009-03-29 00:00:00' AND
'2009-03-29 00:59:59'

ORDER BY data

) foo

GROUP BY 1 ORDER BY 1

-- value = 1.3 NOT OK

-- test

select round(cast( (1.3 + 1.4)::real / 2 as numeric), 1);

-- value = 1.4 OK

Using PostgreSQL 8.3.7 on Windows Server 2008

Thank in advance,

Paolo Saudin