Returns the cardinality of the set identified by key.
返回SET容器的成员数
Parameters
key
Return value
LONG the cardinality of the set identified by key, 0 if the set doesn't exist.
Example
$redis->sAdd('key1' , 'member1');
$redis->sAdd('key1' , 'member2');
$redis->sAdd('key1' , 'member3'); /* 'key1' => {'member1', 'member2', 'member3'}*/
$redis->sCard('key1'); /* 3 */
$redis->sCard('keyX'); /* 0 */
