Question

is it possible to merge 2 arrays without overlapping the same keys ?

I want it to add a new item if a key already exists.

Like that

$a = array(1,2,3,4);
$b = array(3,4,5,6);
merge $a and $b 

desired result is

array(1,2,3,4,3,4,5,6) 

Answer 1

Use array_merge

$a = array(1,2,3,4);
$b = array(3,4,5,6);
$c = array_merge($a,$b);
print_r($c);

Working example here

This is the key phrase from the help :

If the input arrays have the same string keys, then the later value
for that key will overwrite the previous one. If, however, the arrays
contain numeric keys, the later value will not overwrite the original
value, but will be appended.

So this will only work when you have numeric keys