随机函数产生重复结果

Question

I'm working on a script to install sample data into a database. I have a script I coded I call "Generic Data Generator". This PHP file includes a variety of functions to generate random data.

Example function:

// Random number generator.
function gdg_number( $number_start, $number_end ) {

    return rand( $number_start, $number_end );
}

Example query:

function gdg_values( $results ) {

    $values = "";

    for ( $i = 1; $i <= $results; $i++) {
        $values .= "
            '" . gdg_sentence(3,12) . "',
            '" . gdg_multi_paragraphs(1,5,5,8,4,17) . "',
            '" . gdg_multi_paragraphs(1,5,5,8,4,17) . "',
            '" . gdg_number(100,900) . "." . gdg_number(00,99) . "',
            '" . gdg_number(1,20) . "',
            '" . gdg_number(0,50) . "',
            '" . gdg_string(10,10) . "',
            '0'
        ), (";
    }

    return $values;
}

$value = gdg_values( 100 );
$values = substr( $value, 0, -4);

The problem I'm experiencing is when I view the MySQL table after I use the script to insert multiple rows, I notice there is duplicate data entries. Entire rows have the same values for each column.

What could cause the gdg_values() to produce identical results every 3 rows? (Notice, it does this even if I manually copy/paste the $values repeatedly directly into the MySQL query.

Here is the full generic_data_generator.php file.

http://pastebin.com/jjRF8SZd

Here is the full products.php file which is included in the install script for the database to install sample data into the products MySQL table.

http://pastebin.com/TtkstXgS

Answer 1

As stated at Is rand() time-dependent in php?:

Note that the automatic seeding seems to be done with the current number of seconds which means you can get the same results for several runs on a fast server. Either call srand() yourself with a more frequently changing seed or use mt_rand() which doesn't appear to suffer from the problem.

Therefore, you can either use:

function gdg_number( $number_start, $number_end ) {
    return mt_rand( $number_start, $number_end );
}

Or, you can use:

function gdg_number( $number_start, $number_end ) {
    srand();
    return rand( $number_start, $number_end );
}

Both of which should create a different random value more often.