php는 addcslashes() 함수에 의해 추가된 백슬래시를 제거합니다.

<?php
echo stripslashes("Hello World!");
?>

stripcslashes(string)

<?php
$sql = "update book set bookname=&#39;let&#39;s go&#39; where bookid=1";
 echo $sql."<br/>";
 $new_sql = addcslashes($sql,"&#39;");
 echo $new_sql."<br/>";
 $new_sql_01 = stripcslashes($new_sql);
 echo $new_sql_01."<br/>";
 echo addslashes($sql);
?>

update book set bookname='let's go' where bookid=1
update book set bookname=\'let\'s go\' where bookid=1
update book set bookname='let's go' where bookid=1
update book set bookname=\'let\'s go\' where bookid=1