Performs the difference between N sets and returns it.
执行差集操作在N个不同的SET容器之间，并返回结果。这个操作取得结果是第一个SET相对于其他参与计算的SET集合的差集。(Result = SET0 - (SET1 UNION SET2 UNION ....SET N))
Parameters
Keys: key1, key2, ... , keyN: Any number of keys corresponding to sets in redis.
Return value
Array of strings: The difference of the first set will all the others.
返回数组,返回的是第一个SET集合相对于其他集合的差集(first set - (N sets))
Example
$redis->delete('s0', 's1', 's2');
$redis->sAdd('s0', '1');
$redis->sAdd('s0', '2');
$redis->sAdd('s0', '3');
$redis->sAdd('s0', '4');
$redis->sAdd('s1', '1');
$redis->sAdd('s2', '3');
var_dump($redis->sDiff('s0', 's1', 's2'));
Return value: all elements of s0 that are neither in s1 nor in s2.
array(2) {
[0]=>
string(1) "4"
[1]=>
string(1) "2"
}