Php: when array_push encounters static

{Code ...} if staticarray_push is used, the value will not be repeated. In general, if array_push has the same push value, the duplicate value will appear. why is there no repeated value after static is used?

public function find_children_cat($cat_id, $data)    {        static $tem=array();        foreach ($data as $val)        {            if ( $val['parent_id'] == $cat_id )            {                array_push($tem, $val['cat_id']);                $this->find_children_cat($val['cat_id'], $data);            }        }        return $tem;    }

If the value of static array_push is used, there will be no repeated values. In general, if the value of array_push is the same, there will be repeated values;
Why is there no repeated value after static is used?

Reply content:

public function find_children_cat($cat_id, $data)    {        static $tem=array();        foreach ($data as $val)        {            if ( $val['parent_id'] == $cat_id )            {                array_push($tem, $val['cat_id']);                $this->find_children_cat($val['cat_id'], $data);            }        }        return $tem;    }

If the value of static array_push is used, there will be no repeated values. In general, if the value of array_push is the same, there will be repeated values;
Why is there no repeated value after static is used?

The code does not check whether there are repeated values. Normally, the internal variables of a function are released after the function is completed, but when you set the variablestaitcThe static variable exists in the entire function scope. The value of this variable is retained every time you call a function.