连接名称并再次使用concat作为用户名？

I'm trying to pull out information from a database with PHP and have the following query:

$q = "SELECT CONCAT_WS(' ',FirstName,MiddleName,LastName) AS Name,
      (NewCustomerID) AS customerid,
      substring('Firstname',1,1, 'MiddleName'),
      left(MiddleName,1) AS MN,
      (LastName) AS LN
       FROM customer 
       Where FN.MN.LN = 'username'"; 
$r = mysqli_query ($dbc, $q);
$num = mysqli_num_rows($r);

when I run this, I get info back but not the username, which I need:

$q = "SELECT CONCAT_WS(' ',FirstName,MiddleName,LastName) AS Name,
      (NewCustomerID) AS customerid,
      left('Firstname',1) as FN,
      left(MiddleName,1) AS MN,
      (LastName) AS LN 
            FROM customer".

Just stuck, have tried quite a few things and just can't get it to work.

$q = "SELECT CONCAT(left(FirstName,1),left(MiddleName,1),LastName) AS UserName, CONCAT_WS(' ',LastName,FirstName) AS Name, (NewCustomerID) AS customerid FROM customer ";

Since FN, MN, and LN are aliases, you need to use HAVING instead of WHERE.

HAVING FN.MN.LN = 'username'

Though, FN.MN.LN is a syntax error, I assume you meant CONCAT(FN,MN,LN)?

HAVING CONCAT(FN,MN,LN) = 'username'

You are not quoting the query correctly, Firstname is a column name:

SELECT 
    CONCAT_WS(' ',FirstName,MiddleName,LastName) AS Name,
    (NewCustomerID) AS customerid,
    LEFT(Firstname,1) as FN, 
    LEFT(MiddleName,1) AS MN,
    (LastName) AS LN
FROM customer
WHERE CONCAT(FN,MN,LN) = 'username'