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07_Window_Functions/02_RANK.md

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+# RANK()
+
+## Overview
+
+`RANK()` assigns a competition-style rank to each row. Rows with equal
+`ORDER BY` values receive the **same rank**, and the next rank **skips**
+the number of tied rows (like Olympic medal standings).
+
+```
+Ordered values: [10, 20, 20, 40]
+RANK():         [1,  2,  2,  4]
+```
+
+## Learning Objectives
+
+- Assign competition ranks with correctly handled ties.
+- Understand the "gap after a tie" behavior that distinguishes `RANK()`
+  from `DENSE_RANK()`.
+- Filter ranked results using a CTE.
+
+## Prerequisites
+
+- `01_ROW_NUMBER`
+- CTEs (`06_CTEs`)
+
+## Syntax
+
+```sql
+SELECT
+    column_a,
+    RANK() OVER (ORDER BY sort_column) AS rank_value
+FROM table_name;
+```
+
+## Dataset Used
+
+`employes`, `departments`, `locations`
+
+## Examples
+
+See [`02_rank.sql`](./02_rank.sql).
+
+## Real World Applications
+
+- Leaderboards where tied scores should share a position.
+- Sales rankings where multiple reps can tie for the same quota tier.
+
+## Business Use Cases
+
+| Domain | Scenario |
+|---|---|
+| Sales | Rank reps by revenue, allowing ties for shared bonuses |
+| Education | Rank students by exam score with shared placements |
+| Manufacturing | Rank suppliers by defect rate |
+
+## Common Mistakes
+
+- Confusing `RANK()`'s gap behavior with `DENSE_RANK()`'s no-gap behavior.
+- Forgetting that ties are determined entirely by the `ORDER BY` column(s)
+  inside `OVER()` -- not by any other column in the `SELECT` list.
+- Filtering directly on the alias in `WHERE` (same restriction as
+  `ROW_NUMBER()` -- use a CTE).
+
+## Best Practices
+
+- Choose `RANK()` deliberately when business rules require gaps after
+  ties (e.g., "rank 1 and 2 both get gold, next place is rank 3 not 3rd
+  overall position").
+- Document in a comment *why* `RANK()` was chosen over `DENSE_RANK()` --
+  future maintainers should not have to guess.
+
+## Engineering Notes
+
+`RANK()` and `DENSE_RANK()` share the same sorting cost as `ROW_NUMBER()`
+but additionally require a tie-comparison against the previous row's
+`ORDER BY` value, evaluated during the same single pass.
+
+## Practice Questions
+
+1. Assign rank to employees ordered by `emp_id`.
+2. Show employee name and rank.
+3. Show the employee with `rank = 1`.
+4. Show the top 3 ranked employees.
+5. Compare `ROW_NUMBER()` and `RANK()` side by side on `manager_id`.
+
+## Difficulty
+
+Beginner
+
+## Estimated Time
+
+20–25 minutes
+
+## Learning Outcomes
+
+- Correctly predict `RANK()` output on a dataset containing ties.
+- Explain, in an interview, the difference between `RANK()` and
+  `ROW_NUMBER()`.
+
+## Related Topics
+
+- `01_ROW_NUMBER`
+- `03_DENSE_RANK`
+
+## Next Topic
+
+[`03_DENSE_RANK`](../03_DENSE_RANK/README.md)