SETEX key seconds value
将键 key 对应的值设置为字符串值 value，且将键 key 设置为在给定秒（Seconds）后过期。
Set key to hold the string value and set key to timeout after a given number of seconds.
SET mykey value EXPIRE mykey seconds
SETEX is atomic, and can be reproduced by using the previous two commands inside an MULTI / EXEC block. It is provided as a faster alternative to the given sequence of operations, because this operation is very common when Redis is used as a cache.
当秒数 seconds 无效时，将会返回一个错误。
An error is returned when seconds is invalid.