PHP使用PDO从mysql读取大量数据处理详解

$dbh = new pdo($dsn, $user, $pass);
# 关键设置，如果不设置，php依旧会从pdo一次取出数据到php
$dbh->setattribute(pdo::mysql_attr_use_buffered_query, false);
//perpare里的游标属性不是必须的
$sth = $dbh->prepare("select * from `order`", array(pdo::attr_cursor => pdo::cursor_scroll));
$sth->execute();

class test {
 public function test()
 {
  set_time_limit(0);
  $dbms='mysql';  //数据库类型
  $host=c('db_host'); //数据库主机名
  $dbname=c('db_name'); //使用的数据库
  $user=c('db_user');  //数据库连接用户名
  $pass=c('db_pwd');   //对应的密码
  $dsn="$dbms:host=$host;dbname=$dbname";
  $dbh = new pdo($dsn, $user, $pass);
  $dbh->setattribute(pdo::mysql_attr_use_buffered_query, false);
  $sth = $dbh->prepare("select * from `order`");
  $sth->execute();
  $i = 0;

  $newline = php_sapi == 'cli' ? "n" : '<br />';

  foreach ($this->cursor($sth) as $row) {
//   var_dump($row);
   echo $row['id'] . $newline;
   $i++;
  }

  echo "消耗内存：" . (memory_get_usage() / 1024 / 1024) . "m" . $newline;
  echo "处理数据行数：" . $i . $newline;
  echo "success";
 }

 public function cursor($sth)
 {
  while($row = $sth->fetch(pdo::fetch_assoc)) {
   yield $row;
  }
 }
}

$test = new test();
$test->test();

1
... //省略部分id
804288
消耗内存："0.34918212890625m
处理数据行数：254062
success