$a='12345';
$b=12345;
$c=array('x','y','z');

a : string(5) "12345"
a[0] : string(1) "1"
a[1] : string(1) "2"
a[2] : string(1) "3"
a[3] : string(1) "4"
a[4] : string(1) "5"
a[5] : string(0) ""
a[6] : string(0) ""
a[7] : string(0) ""

b : int(12345)
b[0] : NULL
b[1] : NULL
b[2] : NULL

c : array(3) {
[0]=>
string(1) "x"
[1]=>
string(1) "y"
[2]=>
string(1) "z"
}
c[0] : string(1) "x"
c[1] : string(1) "y"
c[2] : string(1) "z"
c[3] : NULL
c[4] : NULL
c[5] : NULL

$a[10]='h'

a : string(11) "12345     h"

$a="あいうeお"

a : string(13) "あいうeお"
a[0] : string(1) ""
a[1] : string(1) ""
a[2] : string(1) ""
a[3] : string(1) ""
a[4] : string(1) ""
a[5] : string(1) ""
a[6] : string(1) ""
a[7] : string(1) ""
a[8] : string(1) ""
a[9] : string(1) "e"
a[10] : string(1) ""
a[11] : string(1) ""
a[12] : string(1) ""
a[13] : string(0) ""
Notice: Uninitialized string offset: 13

SELECT * FROM ordertest ORDER BY field(type,2,1,4,3);
B 2
A 1
D 4
C 3

SELECT * FROM ordertest ORDER BY field(type,4,2);
A 1
C 3
D 4
B 2