15.8 has no exact binary representation, so a test for equality will fail.
Do not use floating point if you want to test for equality. Try DECIMAL
Miguel Figueiredo wrote:
>Hello all,
>
>I have a (probably dumb) question.
>My table "temperatura" has two fields described bellow.
>
>mysql> describe temperatura;
>+-------------+----------+------+-----+---------+-------+
>| Field | Type | Null | Key | Default | Extra |
>+-------------+----------+------+-----+---------+-------+
>| datetime | datetime | YES | | NULL | |
>| temperatura | float | YES | | NULL | |
>+-------------+----------+------+-----+---------+-------+
>2 rows in set (0.00 sec)
>
>
>When I try to select rows with floats, the result is an empty set.
>For example:
>
>mysql> select datetime,temperatura from temperatura where
>datetime="2002-02-08 09:30:00";
>+---------------------+-------------+
>| datetime | temperatura |
>+---------------------+-------------+
>| 2002-02-08 09:30:00 | 15.8 |
>+---------------------+-------------+
>1 row in set (0.00 sec)
>
>----------------------------> got one row :)
>
>mysql>select datetime,temperatura from temperatura where datetime="2002-02-08
>09:30:00" and temperatura=15.8;
>
>Empty set (0.00 sec)
>
>----------> same thing but with the temperatura value, gives me an empy set :(
>
>When I try to select another row but the temperatura field has an integer
>this is what happens:
>
>mysql> select datetime,temperatura from temperatura where
>datetime="2002-01-25 09:40:00";
>+---------------------+-------------+
>| datetime | temperatura |
>+---------------------+-------------+
>| 2002-01-25 09:40:00 | 16 |
>+---------------------+-------------+
>1 row in set (0.00 sec)
>
>-----------> got one row :)
>
>mysql> select datetime,temperatura from temperatura where
>datetime="2002-01-25 09:40:00" and temperatura=16;
>+---------------------+-------------+
>| datetime | temperatura |
>+---------------------+-------------+
>| 2002-01-25 09:40:00 | 16 |
>+---------------------+-------------+
>1 row in set (0.00 sec)
>
>--------------> It works now :/
>
>Does anyone have an idea why this happens? How can I select float numbers?
>
>Best wishes,
>
>Miguel
>
