彼此内部的两个循环不起作用

Question

Hi here is my code :

while ($row = mysql_fetch_array($res)){
    echo "<br>looped firist loop <br>";

    while ($row2 = mysql_fetch_array($res2)){
        echo "<br>looped second loop <br>";

    }

}

it displays

looped firist loop

looped second loop

looped second loop

looped firist loop

looped firist loop

The problem is: in the second loop it loops until the array finishes. Then the second time the first loop is called, it doesn't start from the beginning of the array. So the loop has already reached its max. What is the problem here and how do i solve it?

Answer 1

You need to reset the resultset pointer back to the start of $res2 using mysql_data_seek() if you want to iterate over it a second time:

while ($row = mysql_fetch_array($res)){
    echo "<br>looped firist loop <br>";

    mysql_data_seek($res2, 0);

    while ($row2 = mysql_fetch_array($res2)){
        echo "<br>looped second loop <br>";

    }

}

But the MySQL extension is old and deprecated, and no longer exists in the latest version of PHP, so please move into the 21st century and start using MySQLi or PDO

Nested looping is also hopelessly inefficient, and there are probably better methods to achieve what you want