php-将3个MySQL查询合并为一个

我想做的是拿一张桌子,找出其电子邮件地址为emails.from值的成员的id,然后将其id放在其中.我正在尝试通过使用ID而不是电子邮件地址来提高性能,但是无法完成此任务.

$MysqL = new MysqL();
$MysqL->query('SELECT `from` FROM `emails` ORDER BY `id` ASC' );

while($row = MysqL_fetch_array($MysqL->result)){
    $MysqL2 = new MysqL();
    $MysqL2->query('SELECT `id` FROM `exchange` WHERE `email` = "'.$row['from'].'"');

    $details = MysqL_fetch_assoc($MysqL2->result);


    $MysqL2->query('UPDATE `emails` SET `from` = '.$details['id'].' WHERE `from` = "'.$row['from'].'"');
}

解决方法:

如果我了解您的代码,则可以尝试执行以下操作：

UPDATE     `emails`
INNER JOIN `exchange` ON `exchange`.`email` = `emails`.`from`
SET `emails`.`from` = `exchange`.`id`