Question

I am developing a chat module with JavaScript and php+mysql and I am storing the chat data into a simple table with: id, member1, member2, message, timestamp.
The timestamp column is double(14,4), where I store the timestamp on microseconds level, ex:
1330522898.3137;

My problem is:
When I am comparing this timestamp with another one, like

   SELECT * FROM chat_rows WHERE timestamp >= 1330535168.9548

Only on particular numbers, like this one above, I get 0 rows using operator >= although I have a row with exact same value; This is proved by the almost same query differentiated by operator = :

   SELECT * FROM chat_rows WHERE timestamp = 1330535168.9548

which returns one row;

The workaround for this is to replace the double(14,4) type with varchar but is slower than double;

Also fails only on this server ( my development one ):
Apache/2.2.20 (Ubuntu)
MySQL client version: 5.1.58

On my local it seems that works; – which is windows
Apache/2.2.21 (Win32) mod_ssl/2.2.21 OpenSSL/0.9.8o
Versiunea clientului MySQL: mysqlnd 5.0.8-dev – 20102224 – $Revision: 318113 $

Any thoughts ?

Thanks in advance!

Answer 1

The correct way to do floating-point number comparison is to first decide on an acceptable tolerance for differences between the numbers and then do the comparison against the tolerance value.

MySQL floating point comparison issues