Couriers per Depot
Problem
Table: `Courier`
```text
+------------+---------+
| Column | Type |
+------------+---------+
| courier_id | int |
| depot_id | int |
+------------+---------+
courier_id is the primary key. Each row says which depot a courier works out of.
```
For each courier, report how many couriers in total belong to that courier's depot (the courier themselves included). Return `courier_id` and the count under the column `depot_headcount`. Rows may be in any order.
**Example**
```text
Courier:
+------------+----------+
| courier_id | depot_id |
+------------+----------+
| 11 | 1 |
| 12 | 1 |
| 13 | 1 |
| 21 | 2 |
+------------+----------+
Output:
+------------+-----------------+
| courier_id | depot_headcount |
+------------+-----------------+
| 11 | 3 |
| 12 | 3 |
| 13 | 3 |
| 21 | 1 |
+------------+-----------------+
```
Depot 1 has three couriers, so each of them reports 3. Depot 2 has a single courier, who reports 1.
Tables
Example rows — the live problem includes the full dataset.
| courier_id | depot_id |
|---|---|
| 11 | 1 |
| 12 | 1 |
| 13 | 1 |
Expected output
Your answer should return 4 rows with the columns courier_id, depot_headcount.
Starter code (SQL)
SELECT *
FROM Courier;Solve this SQL question free
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Solution & explanation
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