定义不同的变量然后将它们合并为相等的值并单独回显

$x = 123;
$y = 456;

$x = $y .= 789;

echo "$x<br>";
echo "$y<br>";

In my code here the result is

456789
456789

But this result isn't what i want, Since it is only $y value

What i aim for is to echo it separated like this

123789
456789

Since here i defined $x & $ythen got an equal value, But instead of going $x .= 789 & $y .= 789 I just decided to merge them into one, But i got this only $y value, How can i fix that?

With the following syntax:

$x = $y .= 789;

You're appending 789 to $y, so you get 456789. Then you're assigning this result into $x - so at the end there are two 456789 values.

You cannot simplify this operation in one line - I'd highly suggest to do it in two lines, it's much more clear in understanding.

In your code first you are adding 789 in $y by &y .= 789. Then $y = 456789, After that you assign $y value in $x. So $x value replaced from 123 to 456789.

You have to do it separately.

<?php 
    $x = 123;
    $y = 456;
    $x .= 789; $y .= 789;
    echo "$x<br>";
    echo "$y<br>";
?>

You override the value of $x. Assign them separately. Try this:

$x = 123;
$y = 456;

$x .= 789;
$y .= 789;

echo "$x<br>";
echo "$y<br>";