Php （根据您的需要） SELECT p.post_id, p.title, c.comment_body FROM posts p LEFT JOIN comments c ON c.parent_id = p.post_id while($row = my

（根据您的需要）

SELECT p.post_id, p.title, c.comment_body
FROM posts p
LEFT JOIN comments c
ON c.parent_id = p.post_id

while($row = mysql_fetch_array($result))
  {
  echo $row['title'] . " " . $row['comment_body'];
  echo "<br />";
  }

SELECT p.post_id, p.title, GROUP_CONCAT(c.comment_body)
FROM posts
LEFT JOIN comments c ON c.parent_id = p.post_id
GROUP BY p.post_id

SELECT p.post_id, p.title, GROUP_CONCAT(c.comment_body), count(*) as coment_cnt
FROM
    posts p
        LEFT JOIN comments c ON (p.post_id = c.parent_id)
GROUP BY
    p.post_id

$lastpostid=false;
while ($r=mysql_fetch_assoc($result)) {
  if ($r['post_id']!=$lastpost) {
     print "Post: " . $r['title'] . "<br />\n";
     $comment_id=1;
     $lastpost=$r['post_id'];
  }
  print "Comment # $comment_id : " . $r['comment_body'] . "<br />\n";
  $comment_id++;
}