Tom Duffey <[email protected]> wrote:
> CREATE TABLE test (
> id INTEGER PRIMARY KEY,
> value REAL NOT NULL
> );
>
> INSERT INTO test (id, value) VALUES (1, 10.3884573), (2, 10.3885);
> SELECT * FROM test;
>
> id | value
> ----+---------
> 1 | 10.3885
> 2 | 10.3885
> (2 rows)
>
> At this point you would think you have two equal values.
At this point, try this:
select * from test where value = '10.3885';
id | value
----+---------
2 | 10.3885
(1 row)
Now try this:
select * from test where value = 10.3885;
id | value
----+-------
(0 rows)
Always remember that floating point types are *approximate* data
types; equality often does not behave as you might expect. You're
probably aware of the below issues, but just in case:
select '99999999'::real = ('99999999'::real + '1'::real);
?column?
----------
t
(1 row)
select '.1'::real::float;
float8
-------------------
0.100000001490116
(1 row)
--
Kevin Grittner
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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