Hit the ghost, simple database query, display unknown column ' titletest ' in ' Field list '

Encounter Ghost, simple database query, display unknown column ' titletest ' in ' Field list '
Data fields: ID (self-increment), title (varchar (50), content (Longtext)
Code for
$title = $_post[' title ']; (Value: titletest)
$content =$_post[' content '; (value: Contenttest)
$insert = "INSERT into article (title,content) VALUES (". $title. ', '. $content. ");

Error: Unknown column ' Titletest ' in ' Field list '

Code for
$title = $_post[' title ']; (The value is: Title test) This and the above one more space
$content =$_post[' content '; (value: Contenttest)
$insert = "INSERT into article (title,content) VALUES (". $title. ', '. $content. ");

The error is:
You have a error in your SQL syntax; Check the manual-corresponds to your MySQL server version for the right syntax-use near ' test,contenttest ' in Lin E 1

$insert = "INSERT into article (title,content) VALUES (". $title. ', '. $content. ");
In the $title, $content can be inserted into a string
------Solution--------------------
There is a problem with the statement, so $insert = "INSERT into article (title,content) VALUES (' $title ', ' $content ')";
------Solution--------------------
SQL string has a problem, try this $insert = "INSERT into article (title,content) VALUES ('". $title. "', '". $content. "')";
------Solution--------------------
$insert = "INSERT into article (title,content) VALUES (' $title ', ' $content ')";

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