OT: Retrieve float number from mysql db

[Anonymous Monk]

I have a field in my mysql table type float When I read it with

my $sth = $dbh->prepare("SELECT filed FROM table WHERE id = 1");

I get the value 1679970

when I check the database

"SELECT filed FROM table WHERE id = 1"

I also get 1679970

But when I check it with

"SELECT format(filed,3) FROM table WHERE id = 1"

I get 1679971.000

I do know that the value is in fact 1679971 because I inserted the record myself

And if I retrieve the value with a php script I get 1679971

Any idea why? How can I get the right value 1679971?

[hippo]

This is due to an error in precision when you constructed the table:

use strict;
use warnings;

use Test::More tests => 10;
use DBI;

my $dbuser = shift @ARGV || 'foo';
my $dbpass = shift @ARGV || 'bar';
my $val = 1679971;
my $dbh = DBI->connect ('dbi:mysql:test', $dbuser, $dbpass)
        or die "Conn error: $DBI::errstr";
ok ($dbh->do('CREATE TABLE foo ( bar FLOAT )'), 'Table created');

try_now ($dbh, $val);

$dbh->do ('DROP TABLE foo');
ok ($dbh->do('CREATE TABLE foo ( bar FLOAT (10,0) )'), 'Table created 
+with right precision');
try_now ($dbh, $val);
$dbh->do ('DROP TABLE foo');
$dbh->disconnect;

sub try_now {
        my ($dbh, $val) = @_;
        my $out = 0;
        ok ($dbh->do('INSERT INTO foo VALUE (?)', undef, $val), 'Value
+ inserted');
        ok (my $sth = $dbh->prepare ('SELECT bar FROM foo'), 'Select p
+repared');
        ok ($sth->execute, 'Select executed');
        ($out) = $sth->fetchrow_array;
        is ($val, $out, "Output value $out equals input value $val");
}

Here's my result of running this:

1..10
ok 1 - Table created
ok 2 - Value inserted
ok 3 - Select prepared
ok 4 - Select executed
not ok 5 - Output value 1679970 equals input value 1679971
#   Failed test 'Output value 1679970 equals input value 1679971'
#   at myfloat.t line 30.
#          got: '1679971'
#     expected: '1679970'
ok 6 - Table created with right precision
ok 7 - Value inserted
ok 8 - Select prepared
ok 9 - Select executed
ok 10 - Output value 1679971 equals input value 1679971
# Looks like you failed 1 test of 10.

So, it's nothing to do with Perl and shows that your PHP script is telling porkies.

Update: I suggest you read all about FLOAT in MySQL and particularly the caveats about rounding, precision and exact comparison.

[bitingduck]

Wikipedia also has more details on the limits of precision of 4 byte floats: Single Precision Floating Point. You can only store integers with less than 6 significant digits of precision with the guarantee that you won't suffer approximation. If you need the precision, make sure you choose a type that supports it, and be aware that floating point can get approximated different ways in different implementations that both comply with the same standard.

[choroba]

How did you insert the record? What's the column type in the database?

[Anonymous Monk]

insert into table (field) value (1679971) and data type float

[flexvault]

Dear Monks,

I know little about 'mysql' but what does the following do:

     "SELECT format(filed,3) FROM table WHERE id = 1"

you state:

      I get 1679971.000

That looks to me that 'format(filed,3)' is formating the number to 3 decimal places. What happens if you change it to 'format(filed,0)'?

Hope it helps!

Regards...Ed

[poj]

Try SELECT filed+0 FROM table WHERE id = 1
poj

[Anonymous Monk]

I don't have any answers to you, but only my curiosity ...

• what is the data engine type for the database?
• how was the table created (the create table statement)?
• what are the options set for the database & the table, if any?

[Anonymous Monk]

It is a mysql database

create table mytable (field float);

insert into mytable (field) value (1679971) ;

Mysql is not the problem I think, because if I use php I get 1679971 but with perl i get 1679970

It has to be the way perl represents the float value

[Anonymous Monk]

s/to/for/;

[AnomalousMonk]

s/Anonymous Monk/Registered User/; allows you to correct and update your posts without cluttering up the place with s/to/for/; nodes.