php pdo PDO :: FETCH_LAZY跟踪db游标/指针

What am I doing wrong? How do I track the db cursor if the primary key is not consecutive?

MySQL driver.

 $sql = "SELECT * FROM employees";
 $stmt = $db->query($sql);
 $result = $stmt->fetch(PDO::FETCH_LAZY);
 var_dump($result);

    output:
    object(PDORow)[3]
      public 'queryString' => string 'SELECT * FROM employees' (length=23)
      public 'employeeNumber' => string '1002' (length=4)
      public 'lastName' => string 'Murphy' (length=6)
      public 'firstName' => string 'Diane' (length=5)
      public 'extension' => string 'x5800' (length=5)
      public 'email' => string 'dmurphy@classicmodelcars.com' (length=28)
      public 'officeCode' => string '1' (length=1)
      public 'reportsTo' => null
      public 'jobTitle' => string 'President' (length=9)

$result = $stmt->fetch(PDO::FETCH_ORI_FIRST);
var_dump($result);

output:

    array (size=8)
      'employeeNumber' => string '1056' (length=4)
      'lastName' => string 'Patterson' (length=9)
      'firstName' => string 'Mary' (length=4)
      'extension' => string 'x4611' (length=5)
      'email' => string 'mpatterso@classicmodelcars.com' (length=30)
      'officeCode' => string '1' (length=1)
      'reportsTo' => string '1002' (length=4)
      'jobTitle' => string 'VP Sales' (length=8)

$result = $stmt->fetch(PDO::FETCH_ORI_NEXT);
var_dump($result);

output:

    array (size=16)
      'employeeNumber' => string '1076' (length=4)
      0 => string '1076' (length=4)
      'lastName' => string 'Firrelli' (length=8)
      1 => string 'Firrelli' (length=8)
      'firstName' => string 'Jeff' (length=4)
      2 => string 'Jeff' (length=4)
      'extension' => string 'x9273' (length=5)
      3 => string 'x9273' (length=5)
      'email' => string 'jfirrelli@classicmodelcars.com' (length=30)
      4 => string 'jfirrelli@classicmodelcars.com' (length=30)
      'officeCode' => string '1' (length=1)
      5 => string '1' (length=1)
      'reportsTo' => string '1002' (length=4)
      6 => string '1002' (length=4)
      'jobTitle' => string 'VP Marketing' (length=12)
      7 => string 'VP Marketing' (length=12)

$result = $stmt->fetch(PDO::FETCH_ORI_LAST);
var_dump($result);

output:

    array (size=8)
      0 => string '1088' (length=4)
      1 => string 'Patterson' (length=9)
      2 => string 'William' (length=7)
      3 => string 'x4871' (length=5)
      4 => string 'wpatterson@classicmodelcars.com' (length=31)
      5 => string '6' (length=1)
      6 => string '1056' (length=4)
      7 => string 'Sales Manager (APAC)' (length=20)