Two methods and differences of array merging in PHP

The two methods and differences of array merging in PHP. if you need them, you can refer to the two methods and differences of PHP array merging.
If it is an associated array, as follows:
The code is as follows:
$ A = array (
'Where' => 'uid = 1 ',
'Order' => 'uid ',
);
$ B = array (
'Where' => 'uid = 2 ',
'Order' => 'uid desc ',
);


1. array_merge. if the two arrays have the same key, the next one will overwrite the previous one.
The code is as follows:
$ C = array_merge ($ a, $ B );
Var_export ($ c); // The result is the same as the original $ B.
$ D = array_merge ($ B, $ );
Var_export ($ d); // The result is the same as the original $.

2. "+" operator. if two arrays have the same key, the previous one will overwrite
The code is as follows:
$ C = $ a + $ B;
Var_export ($ c); // The result is the same as the original $.
$ D = $ B + $;
Var_export ($ d); // The result is the same as the original $ B.


If it is a numeric index array, as follows:
The code is as follows:
$ A = array (
1 => '123 ',
2 => '123'
);
$ B = array (
4 => '123 ',
1 => '123'
);

1. array_merge. The effect is similar to the code foreach. each array element is pushed into a new stack.
The code is as follows:
$ C = array_merge ($ a, $ B );
Var_export ($ c );
$ D = array_merge ($ B, $ );
Var_export ($ d );

Output:
Array (
0 => '123 ',
1 => '123 ',
2 => '123 ',
3 => '123 ',
)
Array (
0 => '123 ',
1 => '123 ',
2 => '123 ',
3 => '123 ',
)
2. "+" operator. The effect is similar to the code foreach. each array element is pushed into a new stack. if the same key already exists, it is not processed.
The code is as follows:
$ C = $ a + $ B;
Var_export ($ c );
$ D = $ B + $;
Var_export ($ d );

Output:
Array (
1 => '123 ',
2 => '123 ',
4 => '123 ',
)
Array (
4 => '123 ',
1 => '123 ',
2 => '123 ',
)