碰到鬼了，简单的数据库查询，显示Unknowncolumn'titletest'in'fieldlist'

遇到鬼了，简单的数据库查询，显示Unknown column 'titletest' in 'field list'
数据字段为：id(自增)、title（varchar(50)、content（longtext）
代码为
$title = $_POST['title']; （值为：titletest）
$content =$_POST['content'];（值为：contenttest ）
$insert = "insert into article(title,content) values(".$title.','.$content.")";

错误为：Unknown column 'titletest' in 'field list'

代码为
$title = $_POST['title']; （值为：title test）这个和上面的多一个空格
$content =$_POST['content'];（值为：contenttest ）
$insert = "insert into article(title,content) values(".$title.','.$content.")";

错误为：
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'test,contenttest)' at line 1

将$insert = "insert into article(title,content) values(".$title.','.$content.")";
中的$title, $content 换成字符串就可以插入
------解决方案--------------------
语句有问题， 换成这样 $insert = "insert into article(title,content) values('$title','$content')";
------解决方案--------------------
sql串得有问题，试试这个 $insert = "insert into article(title,content) values('".$title."','".$content."')";
------解决方案--------------------
$insert = "insert into article (title,content) values(‘$title','$content’)";