What are some strange problems encountered when using mysql_query in php?

Ask the php strange question when using mysql_query. $ U; $ result & nbsp; mysql_query (SELECT & nbsp; * & nbsp; FROM & nbsp; user & nbsp; WHERE & nbsp; u) & nbsp; & nbsp; or & nbsp; die (Invali asked php about the strange problem encountered when using mysql_query.

$ Uid = '6 ';
$ Result = mysql_query ("SELECT * FROM user WHERE uid = '$ uid '")
Or die ("Invalid query:". mysql_error ());
Print_r (fetch_array ($ result ));

You can call data uid => 6; username => Anonymous.
However, the following data cannot be called and no error is reported. .

$ Username = 'Anonymous ';
$ Resultt = mysql_query ("SELECT * FROM user WHERE username = '$ username '")
Or die ("Invalid query:". mysql_error ());
Print_r (fetch_array ($ resultt ));

Please advise.
Ps: The database connection is definitely okay. These two pieces of code are run in one file.
------ Solution --------------------
Most of the output statements are encoding problems.

Echo $ resultt = mysql_query ("SELECT * FROM user WHERE username = '$ username'") or die ("Invalid query:". mysql_error ());