03.Redis ZSET

cffttRedis ZSET (Sorted Set) is a collection where:

• value(zset) ≈ { member: score }
• each element is a unique member
• each member has a numeric score (float)
  • e.g., key = topic:123:comments:hot
  • value(zset)={('cmt_777', 532), ('cmt_102', 120), ('cmt_888', 999) ... }
• Redis keeps the set automatically sorted by score (ascending)
  • if scores tie, it sorts by member lexicographically

Core commands

• Add/update score

  • ZADD <key> <score1> <member1> <score2> <member2> ...

• Increment a member’s score

  • ZINCRBY <key> 5 bob

• Get Top N (highest score first)

  • ZREVRANGE <key> 0 9 WITHSCORES

• Get rank

  • rank from high → low: ZREVRANK <key> bob
  • rank from low → high: ZRANK <key> bob

• Get a member’s score

  • ZSCORE <key> alice

• Get members by score range

  • ZRANGEBYSCORE <key> 90 100 WITHSCORES

• Count / size

  • ZCARD <key>
  • ZCOUNT <key> 90 100

• Remove

  • ZREM <key> bob

• Write/update

  • ZINCRBY topic:123:comments:hot 1 cmt_777
    • cmt_777 + 1

• 取 Top N 最热评论（Top 10）

  • ZREVRANGE topic:123:comments:hot 0 9 WITHSCORES

• 分页获取（第 2 页）

  • ZREVRANGE topic:123:comments:hot 10 19 WITHSCORES

• 取某个评论的 rank（排名）和 score