Redis sorted set

When to use

• Enforce uniqueness of elements
• Enforce sort
  
• Needs range based query
• Tabulating a collection in order
• Creating relationships between entities sorted by some criteria
  

Range based query

Z* operations range has inclusive semantic.
And those has zero-based index.

ZCOUNT

inclusive semantic (default)

ZADD products 5 mouse
ZADD products 10 keyboard
ZADD products 25 monitor
ZADD products 40 operating_system
ZADD products 100 cpu

ZCOUNT products 10 25
-- 2 (keyboard: 10, monitor: 25)

exclusive semantic

ZCOUNT products (10 25
-- 1 (monitor: 25)

ZRANGE

ZRANGE is very useful and often used operation.

ZRANGE products 1 1 WITHSCORES
-- [keyboard, 10]

score-based search

ZRANGE products 10 30 BYSCORE WITHSCORES
-- [keyboard, 10, monitor, 25]

index-based search

-- Reverse order before query
ZRANGE products 1 1 REV WITHSCORES
-- [operating_system, 40]

Tips

Redis is key value based NoSQL.
It’s allowed to use duplication for reducing query and enhancing performance.

Suppose we need provide most views on items.
We don’t need only use Hash data which has ${item:id} as key.
We can also use Sorted Set for reducing query and get the highest views items just one query items:views like as shown below.