PHP static variables

Isn't the static variables of PHP stored only in one copy? I tried the following code today. I have some doubts: {code...} since it is only a copy in the memory, calling it again is similar to direct reference. why is $ num assigned 20 for the first time? Shouldn't the result of the first running be 4950? isn't the static variable of PHP saved only in one copy? I tried to explain the following code today.

function test(){    static $sum = 0;    static $sum = 20;    for ($i=0; $i < 100; $i++) {         $sum = $sum + $i;     }    echo  $sum;}echo "
";    test();//4970echo "
";    test();//9920echo "
";    test();//14870        
Since there is only one copy in the memory and the re-call is similar to direct reference, why is $ num assigned 20 for the first time?
The first running result should not be 4950.
                                                    
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Isn't the static variables of PHP stored only in one copy? I tried to explain the following code today.
function test(){    static $sum = 0;    static $sum = 20;    for ($i=0; $i < 100; $i++) {         $sum = $sum + $i;     }    echo  $sum;}echo "
";    test();//4970echo "
";    test();//9920echo "
";    test();//14870        
Since there is only one copy in the memory and the re-call is similar to direct reference, why is $ num assigned 20 for the first time?
The first running result should not be 4950.
                                                                
                                    
$ I = 1; $ I <101
...
// Result: 4950;
                                        
                                    
It can be understood as the row with the value of 20. it overwrites the row with the upper face value of 0. because the variable names are the same, the initialization time is 20.