#1126 Adding support for command ZRANK (#1137)

docs/src/content/docs/commands/ZRANK.md

@@ -0,0 +1,81 @@
+---
+title: ZRANK
+description: The `ZRANK` command in DiceDB is used to determine the rank of a member in a sorted set. It returns the position of a member in the sorted set, with the lowest score having rank 0.
+---
+
+## Syntax
+
+```bash
+ZRANK key member [WITHSCORE]
+```
+
+## Parameters
+
+| Parameter   | Description                                                                 | Type   | Required |
+|-------------|-----------------------------------------------------------------------------|--------|----------|
+| `key`       | The key of the sorted set.                                                  | String | Yes      |
+| `member`    | The member whose rank is to be determined.                                  | String | Yes      |
+| `WITHSCORE` | If provided, the command will also return the score of the member.          | String | No       |
+
+## Return values
+
+| Condition                                      | Return Value                                      |
+|------------------------------------------------|---------------------------------------------------|
+| If member exists in the sorted set             | Integer (rank of the member)                      |
+| If `WITHSCORE` option is used                  | Array (rank and score of the member)              |
+| If member or key does not exist                | `nil`                                             |
+
+## Behaviour
+
+- The `ZRANK` command searches for the specified member within the sorted set associated with the given key.
+- If the key exists and is a sorted set, the command returns the rank of the member based on its score, with the lowest score having rank 0.
+- If the `WITHSCORE` option is provided, the command returns both the rank and the score of the member as an array.
+- If the key does not exist or the member is not found in the sorted set, the command returns `nil`.
+
+## Errors
+
+1. `Wrong type of value or key`:
+   - Error Message: `(error) WRONGTYPE Operation against a key holding the wrong kind of value`
+   - Occurs when the specified key exists but is not associated with a sorted set.
+
+2. `Invalid syntax or number of arguments`:
+   - Error Message: `(error) ERR wrong number of arguments for 'zrank' command`
+   - Occurs if the command is issued with an incorrect number of arguments.
+
+3. `Invalid option`:
+   - Error Message: `(error) ERR syntax error`
+   - Occurs if an invalid option is provided.
+
+## Example Usage
+
+### Basic Usage
+
+Retrieve the rank of `member1` in the sorted set `myzset`:
+
+```bash
+127.0.0.1:7379> ZADD myzset 1 member1 2 member2 3 member3
+(integer) 3
+127.0.0.1:7379> ZRANK myzset member1
+(integer) 0
+127.0.0.1:7379> ZRANK myzset member3
+(integer) 2
+```
+
+### Using WITHSCORE Option
+
+Retrieve both the rank and the score of `member2` in the sorted set `myzset`:
+
+```bash
+127.0.0.1:7379> ZADD myzset 1 member1 2 member2
+(integer) 2
+127.0.0.1:7379> ZRANK myzset member2 WITHSCORE
+(integer) [1, 2]
+```
+
+## Best Practices
+
+- Use `ZRANK` in combination with `ZADD` and `ZSCORE` for efficient management of sorted sets and leaderboards.
+
+## Notes
+
+- This command is particularly useful for implementing leaderboards, pagination in ranked lists, and analytics on data distribution.