Hello.
If the space is so important to you, what do you think about 'LIKE' operator?
It seems to work corectly and it is able to use indexes. See:
create table fff (x float, key(x));
insert into fff values(0.1);
insert into fff values(0.11);
............................
select * from fff where x like 0.1;
+------+
| x |
+------+
| 0.1 |
| 0.1 |
| 0.1 |
+------+
mysql> explain select * from fff where x like 0.1 \G;
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: fff
type: index
possible_keys: x
key: x
key_len: 5
ref: NULL
rows: 16
Extra: Using where; Using index;
Jacek Becla <[EMAIL PROTECTED]> wrote:
> Hi,
>
> I'm having problems with floats while doing comparisons.
>
> create table fff (x float);
> create table ddd (x double);
> insert into fff (0.1);
> insert into ddd (0.1);
>
> "select * from ddd where x = 0.1" correctly returns one row, but
> "select * from fff where x = 0.1" does not return anything.
>
> I found on many websites that "If you are comparing FLOAT or
> DOUBLE columns with numbers that have decimals, you can't use '='.
> This problem is common in most computer languages because
> floating-point values are not exact values. In most cases,
> changing the FLOAT to a DOUBLE will fix this."
>
> This solution is fine as long as involved data size is relatively small.
> We are planning to store ~500 millions rows per day, each containing
> many floats. Switching to double is not a viable option due to space
> overhead. I wonder if anyone has a better suggestion how to solve it.
>
> Thanks,
> Jacek
>
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