SETSet a key's string value with optional TTL and existence conditions.
| 语法 | SET key value [EX seconds|PX milliseconds] [NX|XX] |
| 分组 | string |
| 参数个数 | -3 |
| 起始版本 | 1.0.0 |
| 标志 | write |
| 复杂度 | O(1) |
| Redis 兼容性 | differs: only NX / XX / EX / PX are parsed — KEEPTTL, EXAT, PXAT, GET and the IFEQ family are a syntax error; a repeated expire option is silently accepted last-one-wins instead of erroring |