PHP Remove All Non-alphanumeric Characters Except Apostrophes - preg-replace

Question

$keywords = explode("\n",$_POST['keywords']);
//Inserting into Database
foreach($keywords as $key => $keyword){
$keyword = strtolower(trim($keyword));
$keyword = preg_replace("/[^A-Za-z0-9' ]/", "", $keyword);
$keyword = preg_replace("/\s+/", " ", $keyword);
$insertkeywords = "INSERT IGNORE INTO kwdb (keyword) VALUES ('$keyword')";
mysql_query($insertkeywords);
}
I can't for the life of me figure out why this code won't insert the keywords into the database when I have an apostrophe in the:
"/[^A-Za-z0-9' ]/"
But when I remove it to be:
"/[^A-Za-z0-9 ]/"
This script inserts records into the database.
What am I trying to do?
I have a textarea on a form. For each keyword on a new line, I explode based on the \n. I want to remove all non-letter and non-number characters from the keywords but don't want apostrophes to be removed.
I basically want all keywords to be lower-case with leading, trailing and extra white spaces - 2 or more blank spaces trimmed down to one - removed along with any non-letter and non-number characters except for apostrophes.

Answer 1

You need to escape your keyword: $insertkeywords = "INSERT IGNORE INTO kwdb (keyword) VALUES ('".mysql_real_escape_string($keyword)."')";

Answer 2

Thank you clover. Without your help, it would have taken me many hours to figure that one out! I ended up using mysqli_real_escape_string instead of mysql_real_escape_string because mysql_real_escape_string says it is deprecated as of PHP 5.5.0. As a result, I had to change it up a bit but the below code seems to work great for me so far (in case anyone else runs across this).
$con = mysqli_connect("localhost","username","password");
if (!$con)
{
die('Could not connect: ' . mysqli_error());
}
else
{
echo "Connected Successfully!";
}
//select database
mysqli_select_db($con, "test");
$keywords = explode("\n",$_POST['keywords']);
//Inserting into Database
foreach($keywords as $key => $keyword){
$keyword = preg_replace("/[^A-Za-z0-9' ]/", " ", $keyword);
$keyword = preg_replace("/\s+/", " ", $keyword);
$keyword = strtolower(trim($keyword));
//$insertkeywords = "INSERT IGNORE INTO kwdb (keyword) VALUES ('$keyword')";
$insertkeywords = "INSERT IGNORE INTO kwdb (keyword) VALUES ('".mysqli_real_escape_string($con, $keyword)."')";
mysqli_query($con, $insertkeywords);
}