Perl DBI / MySQL - can't for specific float values - mysql

Question

I've got a problem with my perl and mysql code.
I have a database with a table "STORAGEDATA". In this table I have the column "CLOSETIME" with the datatype "double", which stores an epoch timestamp as a float value (the floating part represents milliseconds).
I now have the problem, that I can't find some of those values with a SELECT-Statement.
MySQL-Example:
SELECT * FROM STORAGEDATA WHERE CLOSETIME = 1360021730.666;
-- This will find the data I am looking for
SELECT * FROM STORAGEDATA WHERE CLOSETIME = '1360021730.666';
-- This works, too
SELECT * FROM STORAGEDATA WHERE CLOSETIME = 1360209405.574;
-- This will find my data, too
SELECT * FROM STORAGEDATA WHERE CLOSETIME = '1360209405.574';
-- But this does not find anything.
The searched values definitly exists in the table and are exactly saved as the values shown above (no trailing zeros or something).
Now I've got the problem that I don't know how to fetch the data using perl dbi.
Perl-Example:
my $sql = 'SELECT * FROM STORAGEDATA WHERE CLOSETIME = ?';
my #args = (1360209405.574);
# $dbh is a database-handler, providing the DBI-functionality
my $sth = $dbh->prepare($sql);
my #data;
if ($sth) {
$sth->execute(#args);
while ( my $dataset = $sth->fetchrow_hashref() ) { push #data, $dataset; }
}
This won't find anything, it seems like DBI inserts the arguments as strings. When I put my quittime directly into the code, it works:
my $sql = 'SELECT * FROM STORAGEDATA WHERE CLOSETIME = 1360209405.574';
my #args = ();
# $dbh is a database-handler, providing the DBI-functionality
my $sth = $dbh->prepare($sql);
my #data;
if ($sth) {
$sth->execute(#args);
while ( my $dataset = $sth->fetchrow_hashref() ) { push #data, $dataset; }
}
This will work, but that's not what I want to do. When I use DBIx, the problem is still the same. I could use "LIKE" instead of "=" to compare, but this would extremely slow down the query.
I tried to change the datatype for CLOSETIME to "Decimal(13,3)", but this didn't change anything.
I run MySQL in version 5.1.73.
Do you have any suggestions how I can solve this problem?

Answer 1

Solution
Either upgrade MySQL, or explicitly specify your predicate's type in the SQL itself:
SELECT * FROM STORAGEDATA WHERE CLOSETIME = CAST(? AS DECIMAL(13,3))
^^^^^^^^^^^^^^^^^^^^^^^^
Rationale
To my thinking, you show us the heart of the matter right away:
SELECT * FROM STORAGEDATA WHERE CLOSETIME = 1360209405.574;
-- This will find my data, too
SELECT * FROM STORAGEDATA WHERE CLOSETIME = '1360209405.574';
-- But this does not find anything.
Huh? That's not what I'd expect. This appears to be a bug in MySQL 5.1, remedied in at least 5.5 (possibly earlier). Smallest demonstration I could think of:
SELECT VERSION(), '1360209405.574' = 1360209405.574 AS "str-num comparison";
-- Under 5.5, TRUE: http://sqlfiddle.com/#!2/e705e6/1
SELECT VERSION(), '1360209405.574' = 1360209405.574 AS "str-num comparison";
-- Under 5.1, FALSE: http://sqlfiddle.com/#!8/e705e/1
Under 5.1, explicitly CASTing to DECIMAL worked for me.

Answer 2

try turning on bind type guessing
my $dbh= DBI->connect('DBI:mysql:test', 'username', 'pass',
{ mysql_bind_type_guessing => 1})
- OR after handle creation
$dbh->{mysql_bind_type_guessing} = 1;

Answer 3

You can use bind_param: https://metacpan.org/pod/DBI#bind_param
$sth->bind_param(1, $args[0], SQL_DOUBLE);
$sth->execute;