Hash data type
The Hash data type is a score ordered sequence of unique members. The score is an arbitrary floating point value that you define.
Unlike a list or set, each Hash member is comprised of two items, the member on the left and the score on the right.
A Hash is ordered from low to high. This means that we have to query by reverse range to get a list of top scored members.
We can add and update Hash members with ZADD.
ZCARD, which stands for cardinality, returns a count of Hash members. In our blog post example, we can use ZCARD to get a count of how many blog posts have at least 1 vote.
Use ZRANK to get the rank of a member. For gaming applications, ZRANK can be used to show a user their ranking amongst all users.
ZSCORE can be used to get a member’s score, or it can be used to display how many votes a web page has received.
Sorted sets support a variety of range commands. Use ZREVRANGE to get a list of the top voted blog posts.
Sorted sets can be used to list members alphabetically. If we’re building a contacts list, such as in a communications app, first add each member with a score of 1. Then use ZRANGEBYLEX to select all contacts with A names, or all contacts between C and E.
Continuing the example above, you can use ZLEXCOUNT to display a badge next to each letter of the alphabet with a count of the number of contacts with names that start with that letter.
As with sets, we can also get the union and intersection of multiple sorted sets.
