Two methods and differences of array merging in PHP

Two methods and differences of PHP array merging
If it is an associative array, the following:

Copy CodeThe code is as follows:
$a = Array (
' WHERE ' = ' uid=1 ',
' Order ' = ' uid ',
);
$b = Array (
' WHERE ' = ' uid=2 ',
' Order ' = ' uid desc ',
);

1. Array_merge, if two arrays have the same key, the latter one will overwrite the previous

Copy CodeThe code is as follows:
<?php
$c = Array_merge ($a, $b);
Var_export ($c);//The result is the same as the original $b
$d = Array_merge ($b, $a);
Var_export ($d);//The result is the same as the original $ A

2. The "+" operator, if the two array has the same key, the previous one will overwrite the following

Copy CodeThe code is as follows:
<?php
$c = $a + $b;
Var_export ($c);//The result is the same as the original $ A
$d = $b + $a;
Var_export ($d);//The result is the same as the original $b

If it is a numeric index array, as follows:

Copy CodeThe code is as follows:
$a = Array (
1 = ' 1111111 ',
2 = ' 222222222 '
);
$b = Array (
4 = ' 33333333333 ',
1 = ' 444444444 '
);

1. Array_merge. The effect resembles code foreach each array element and then presses each element into a new stack

Copy CodeThe code is as follows:
<?php
$c = Array_merge ($a, $b);
Var_export ($c);
$d = Array_merge ($b, $a);
Var_export ($d);

Output:
Array (
0 = ' 1111111 ',
1 = ' 222222222 ',
2 = ' 33333333333 ',
3 = ' 444444444 ',
)
Array (
0 = ' 33333333333 ',
1 = ' 444444444 ',
2 = ' 1111111 ',
3 = ' 222222222 ',
)
2. The "+" operator. The effect is similar to the code foreach each array element, then presses each element into a new stack, and if the same key already exists, does not process

Copy CodeThe code is as follows:
<?php
$c = $a + $b;
Var_export ($c);
$d = $b + $a;
Var_export ($d);

Output:
Array (
1 = ' 1111111 ',
2 = ' 222222222 ',
4 = ' 33333333333 ',
)
Array (
4 = ' 33333333333 ',
1 = ' 444444444 ',
2 = ' 222222222 ',
)

Two methods and differences of array merging in PHP