Problems related to changing PDO from SQLITE to MYSQL

I have written a small code to use PDO to connect to SQLITE. now I am connected to MYSQL. the Fatalerror: Calltoamemberfunctionfetch () error is returned () onanon-object prompts no fetch method. how can this problem be solved? Corresponding line of code: PDO connection from SQLITE to MYSQL
Please refer
I wrote a small code and used PDO to connect to SQLITE. everything works.
An error is reported when I connect to MYSQL.
Fatal error: Call to a member function fetch () on a non-object
What should I do if there is no fetch method?

Corresponding line of code:
$ SQL = "select * from url where long = '$ _ POST [url]'"; // query whether the url is already in the database
$ Query = $ db-> query ($ SQL );
$ Row = $ query-> fetch ();

------ Solution --------------------
$ SQL = "select * from url where 'long' = '$ _ POST [url]'";