ZADDAdd members with scores to a sorted set, with conditional flags.
| Syntax | ZADD key [NX|XX] [GT|LT] [CH] [INCR] score member [score member ...] |
| Group | zset |
| Arity | -4 |
| Since | 1.0.0 |
| Flags | write |
| Complexity | O(M log N) — O(1) hash insert plus O(log N) tree insert per member |
| Redis compatibility | full |