array_column null，但给出了2d数组

Question

为什么array_column警告我它在此代码段中收到null？它似乎对$ hLA里面收到的内容感到愤怒，但它显然是一个二维阵列。我收到的错误是：“PHP警告：array_column（）期望参数1为数组，给定为”

来自var_dump $ hLA的值：

$hL = pg_query("SELECT * FROM hubs");
$hLA = pg_fetch_all($hL);

function updateArticles($tP){
    global $hLA;
    $hmkey = array_search($tP['hm'], array_column($hLA, 'hm'));
}

array(4) {
  [0]=>
  array(6) {
    ["hm"]=>string(12) "5CCF7F33B58C"
    ["hx"]=>string(1) "9"
    ["hy"]=>string(2) "14"
    ["zn"]=>string(6) "T1"
    ["r"]=>string(1) "n"
    ["a"]=>string(1) "n"
  }
  [1]=>
  array(6) {
    ["hm"]=>string(12) "5CCF7FACBBFD"
    ["hx"]=>string(1) "1"
    ["hy"]=>string(1) "1"
    ["zn"]=>string(4) "R"
    ["r"]=>string(1) "y"
    ["a"]=>string(1) "n"
  }
  [2]=>
  array(6) {
    ["hm"]=>string(12) "5CCF7FADCE84"
    ["hx"]=>string(1) "8"
    ["hy"]=>string(1) "5"
    ["zn"]=>string(4) "Exit"
    ["r"]=>string(1) "n"
    ["a"]=>string(1) "y"
  }
}