php如何向数据库添加图片

/*链接数据库*/

// 1.转为普通字符
$file = file_get_contents('test.jpg');
$base64_str = base64_encode($file);
$len = strlen($base64_str);
$step = ceil($len/50000);

for ($i=0; $i <$step ; $i++) { 
    $substr = substr($base64_str, $i*50000,50000);
    $sql = "INSERT INTO b64_img VALUES( null,1,1,$i,&#39;$substr&#39;) ";
    $res = mysqli_query($link,$sql);
}

/*链接数据库*/


$sql = "SELECT * FROM b64_img WHERE imgid = 1 ORDER BY bakid ASC ";
$res =    mysqli_query($link,$sql);
$data = array();
$imgStr = '';

while ($row = mysqli_fetch_assoc($res)) {
    $imgStr .= $row['bstr']    ;
}

$binaryStr = base64_decode($imgStr);
file_put_contents("ThisImg.jpg", $binaryStr);