排序前：
Array
(
[0] => Array
(
[name] => 龍
[age] => 2017-02-28
)
[1] => Array
(
[name] => 龍2
[age] => 2017-03-14
)
[2] => Array
(
[name] => 小3
[age] => 2017-05-09
)
[3] => Array
(
[name] => 龍4
[age] => 2017-02-03
)
[4] => Array
(
[name] => 龍5
[age] => 2017-03-23
)
[5] => Array
(
[name] => 龍6
[age] => 21
)
)
array_multisort(array_column($arr,'age'),SORT_DESC,$arr);
print_r($arr);
排序後：
Array
(
[0] => Array
(
[name] => 龍6
[age] => 21
)
[1] => Array
(
[name] => 小3
[age] => 2017-05-09
)
[2] => Array
(
[name] => 龍5
[age] => 2017-03-23
)
[3] => Array
(
[name] => 龍2
[age] => 2017-03-14
)
[4] => Array
(
[name] => 龍
[age] => 2017-02-28
)
[5] => Array
(
[name] => 龍4
[age] => 2017-02-03
)
)
其中 array_column(數組,數組中的某個鍵值) 從多維數組中取出某個鍵值的一列 返回一個一維數組；
array_multisort(數組(一維數組),排序方式(SOTR_ASC,SOTR_DESC),其他數組(可以是二維的))