PHP rand函数给出空值 - 仍然无法正常工作

I have this little tid-bit of my code, which is eventually sent to a MySQL database. The rest of the code is sound, but this code likes to give me empty data some of the time. Is there any way to prevent this from happening?

Edit: Here's the whole chunk

//random Species
$sp_one = mt_rand(1,10);    
$one_species = "Water Leaper";

//random Genetics

if($one_species == "Water Leaper")
{
    $one_gene = mt_rand(1,5);

    if($one_gene < 3)
    {
        $one_genetics = "1";
    }

    else if($one_gene < 5)
    {
        $one_genetics = "2";
    }

    else
    {
        $one_genetics = "3";
    }
}

//random Gender
$one_sex_num = mt_rand(1,2);

if($one_sex_num == 1)
{
    $one_gender = "Female";
}

if($one_sex_num == 2)
{
    $one_gender = "Male";
}

//Entering it
$sql="INSERT INTO creatures (species, sex, location, genetics)
VALUES('{$one_species}','{$one_gender}', 's1','{$one_genetics}')";

mysqli_query($con,$sql);

First, your if clauses seem a bit redundant. More concise code:

if ($one_gene <3)      { $one_genetics = "1"; }
elseif ($one_gene <5)  { $one_genetics = "2"; }
else                   { $one_genetics = "3"; }

This should always return a value - if everything else fails, "3".

Maybe better even:

$one_genetics = ($one_gene + 1) / 2; // integer division

I don't know what you are doing exacly but maby you can take a look at this:

<?php

    $animals = array();

    $animals[] = array('dog', 78, array('Komondor','Old English Sheepdog'));    
    $animals[] = array('Drosophila', 8, array('Vestigal','Ebony')); 

    $number_animals = count($animals) - 1;
    $list_size = 30;

    for($q = 1; $q <= $list_size; $q++){

        $rand = rand(0, $number_animals);
        $animal = $animals[$rand];

        $number_species = count($animal[2]) - 1;

        $rand = rand(0, $number_species);
        $randsex = rand(0, 1);

        $species = $animal[2][$rand];
        $sex = ($randsex ? 'male' : 'female');
        $genes = $animal[1];

        echo "$q: $species - $sex - $genes <br>";
    }

?>

See a live demo at: here

It pics random animals with specs if you want you can modify to your own wishes.