About PHP static variables

Don’t PHP’s static variables only store one copy in memory? I tried the following code today and I have some questions

<code>function test(){
    static $sum = 0;
    static $sum = 20;
    for ($i=0; $i < 100; $i++) { 
        $sum = $sum + $i; 
    }
    echo  $sum;
}
echo "<pre class="brush:php;toolbar:false">";
    test();//4970
echo "<br />";
    test();//9920
echo "<br />";
    test();//14870
    
    </code>

Since there is only one copy in the memory, calling it again is similar to a direct reference, so why was $num assigned to 20 for the first time?
Shouldn’t the result of the first run be 4950?

Reply content:

Don’t PHP’s static variables only store one copy in memory? I tried the following code today and I have some questions

<code>function test(){
    static $sum = 0;
    static $sum = 20;
    for ($i=0; $i < 100; $i++) { 
        $sum = $sum + $i; 
    }
    echo  $sum;
}
echo "<pre class="brush:php;toolbar:false">";
    test();//4970
echo "<br />";
    test();//9920
echo "<br />";
    test();//14870
    
    </code>

Since there is only one copy in the memory, calling it again is similar to a direct reference, so why was $num assigned to 20 for the first time?

Shouldn’t the result of the first run be 4950?

$i =1;$i<101

…

//Result: 4950;

It can be understood that the line with the value 20 overwrites the line with the value 0 above. Because the variable names are the same, it is 20 when initialized.