PHP join関数で配列の要素同士をカンマ区切りで結合するサンプル
環境
PHP 8.1.2
Ubuntu 22.04.1 LTS
構文
$result = join(“,", $対象の配列名);
join()の第１引数にカンマの文字列（","）、第２引数に対象の配列を指定します。
配列(array)の要素同士をカンマ区切りで結合して１つの文字列に変換するには、join()を使います。
使用例
<?php
$ns = [ "study", "skill", "become", "smart", "arkgame"];
$result = join(",", $ns);
echo $result
?>
<?php
$ns = [ "study", "skill", "become", "smart", "arkgame"];
$result = join(",", $ns);
echo $result
?>
<?php
$ns = [ "study", "skill", "become", "smart", "arkgame"];
$result = join(",", $ns);
echo $result
?>
実行結果
study,skill,become,smart,arkgame