php获取数组中单列值

<?php
// 表示由数据库返回的可能记录集的数组
$a = array(
 array(
  &#39;id&#39; => 5698,
  &#39;first_name&#39; => &#39;Bill&#39;,
  &#39;last_name&#39; => &#39;Gates&#39;,
 ),
 array(
  &#39;id&#39; => 4767,
  &#39;first_name&#39; => &#39;Steve&#39;,
  &#39;last_name&#39; => &#39;Jobs&#39;,
 )
 array(
  &#39;id&#39; => 3809,
  &#39;first_name&#39; => &#39;Mark&#39;,
  &#39;last_name&#39; => &#39;Zuckerberg&#39;,
 )
);
$last_names = array_column($a, &#39;last_name&#39;, &#39;id&#39;);
print_r($last_names);
?>

Array
(
 [5698] => Gates
 [4767] => Jobs
 [3809] => Zuckerberg
)