mysql,concat连接字符串
可以用 $rem = "concat(content,'$rem')"; 

php代码：

$rem = '<hr><!-\'flag_ins\'--><div class="xiaoqu_pic"><h4>小区图:</h4>
<img src="/image/fangyuan.jpg" /><br/>
<img src="/image/fangyuan.jpg" /><br/>
<img src="/image/fangyuan.jpg" /><br/>
<img src="/image/fangyuan.jpg" /><br/>';

$rem = str_replace("'","\'",$rem);
$rem = "concat(content,'$rem')"; 
$sql = "UPDATE archivesX1 SET content=$rem WHERE aid='593009'";
$q = $db->query($sql);
var_export($q);