php将数组转化成拼接IN字符串实现mysql使用where in 用法

/* 拼接成in格式: IN('a','b','c')
   * @access   public
   * @param    mix      $list      列表数组或字符串
   * @return   string
*/
function create_in($list = '')
{
  if (empty($list)) {
    return " IN ('') ";
  } else {
    $str = joinString($list);
    return trim($str) == '' ? " IN ('') " : " IN (" . $str . ") ";
  }
}
/*
 * @name 拼接字符串，并且去掉重复项: 'a','b','c'
 * @access   public
 * @param    mix      $list      列表数组或字符串
 * @param    bool  $res_arr 是否返回数组
 * @return   string
 */
function joinString($list = '', $delimiter = ',', $res_arr = false)
{
  if (!is_array($list)) {
    $list = explode($delimiter, $list);
  }
  $list = array_unique($list);
  $arr  = array();
  foreach ($list AS $v) {
    if (is_array($v)) {
      foreach ($v as $key => $val) {
        $arr[] = "'" . $val . "'";
      }
    } elseif ($v !== '') {
      $arr[] = "'$v'";
    }
  }
  if ($res_arr) {
    return $arr;
  }
  return count($arr) == 0 ? " " : join($delimiter, $arr);
}