仅当姓氏不唯一时，才显示名字

Question

How to print the last name only, whenever it is unique? Else print the full name as 'last name, first name'.

Example: In the database, you have: Ace Perez, Dan Perez, James Perez and Dan Bond. It should display something like:

Perez Ace Perez Dan Perez James Bond

It will only display Bond instead of Bond Dan, since it's a unique last name.

Here is my code snippet:

<?php
$display = "SELECT * FROM main ORDER BY lastName ASC, firstName ASC";
$result = @mysql_query($display)or die(mysql_error());
while($row = mysql_fetch_array($result)){
    $lastName = $row['lastName'];
    $firstName = $row['firstName'];
    $score = $row['score'];
    $totalScore = $row['totalScore'];
    $percentage = ($score/$totalScore)*100;
    echo "<tr>";
        echo "<td align='left'> $lastName </td>";
        echo "<td align='left'> $firstName </td>";
        echo "<td align='left'> $percentage </td>";
    echo "</tr>";
}
    echo "</table>";
?>

Edit: Sorry, I'm quite new here. The snippet should be displaying properly now! :)

Answer 1

You can do this by counting the number of matches on the last name. Then use this for a conditional select :

select m.lastname, (case when cnt > 1 then m.firstname end) as firstname
from main m join
     (select lastname, count(*) as cnt
      from main
      group by lastname
     ) ml
     on m.lastname = ml.lastname;

Answer 2

If you have a primary key, you could use a simple query with CASE and EXISTS ;

SELECT 
  lastname, 
  CASE WHEN EXISTS 
    ( SELECT 1 FROM test t2 WHERE t1.lastname=t2.lastname AND t1.id<>t2.id )
  THEN firstname ELSE '' END firstname
FROM test t1

An SQLfiddle to test with .