Split two delimited strings into arrays of words, merge, then remove duplicates

I'm struggling to remove duplicates words found within two strings.

When I call array_unique, the duplicated words are not removed.

$a = 'mysql string 1';// basically words A, B, C
$b = 'mysql string 2';// basically words D, A, E
$a_b_array = array($a, $b);
sort($a_b_array);
$a_b_string = implode("\n", array_unique($a_b_array));

echo $a_b_string; //returns $a and $b with duplicated data

Expected result would be: A, B, C, D, E

First of all you are dealing with an array of two elements. You will need to explode each element into arrays first.

<?php
// define your inputs    
$a = 'A, B, C';
$b = 'D, A, E';

// explode the string into arrays and merge them
$a_b_array = array_merge(explode(",", $a), explode(",", $b));

// trim off any pesky leading or trailing spaces from the elements
$a_b_array = array_map("trim", $a_b_array);

sort($a_b_array);
// tape the elements back together separated by a newline
$a_b_string = implode("\n", array_unique($a_b_array));
echo $a_b_string;