问号在MySQL中“ WHERE column =？”的意义是什么？?mysql

我剖析了一些代码，并发现了这一点，

$sql = 'SELECT page.*, author.name AS author, updator.name AS updator ' . 'FROM '.TABLE_PREFIX.'page AS page ' . 'LEFT JOIN '.TABLE_PREFIX.'user AS author ON author.id = page.created_by_id ' . 'LEFT JOIN '.TABLE_PREFIX.'user AS updator ON updator.id = page.updated_by_id ' . 'WHERE slug = ? AND parent_id = ? AND (status_id='.Page::STATUS_REVIEWED.' OR status_id='.Page::STATUS_PUBLISHED.' OR status_id='.Page::STATUS_HIDDEN.')'; 我想知道“？” 在WHERE语句中执行。它是某种参数持有人吗？