What Kinds of Transactions Are Customers Making?
Northline Bank's operations team is planning capacity for the next quarter and wants to see the shape of the month's traffic: how many transactions of each kind the systems handled, as raw counts.
Each transaction carries a type label. The team wants the answer built from whatever labels actually appear in the data, so that a kind they have not thought of — a fee, a reversal — turns up on the list by itself instead of being quietly left out.
transactions — one row per transaction. amount is in dollars and is negative for money leaving the account. type is a short label.
| id | customer_id | amount | type | txn_date |
|---|---|---|---|---|
| 1 | 1 | 500 | deposit | 2023-07-01 |
| 2 | 1 | -120 | withdrawal | 2023-07-03 |
| 3 | 2 | 1000 | deposit | 2023-07-02 |
| 4 | 2 | -300 | withdrawal | 2023-07-05 |
| 5 | 3 | 250 | deposit | 2023-07-04 |
| 6 | 3 | -600 | withdrawal | 2023-07-06 |
| 7 | 4 | 800 | deposit | 2023-07-07 |
| 8 | 4 | -450 | withdrawal | 2023-07-08 |
| 9 | 5 | 2000 | deposit | 2023-07-09 |
| 10 | 5 | -1500 | withdrawal | 2023-07-10 |
| 11 | 1 | -200 | transfer | 2023-07-11 |
| 12 | 3 | 400 | deposit | 2023-07-12 |
The table already exists in the database — there is nothing to create or load.
Task: Write a query returning two columns, type and num_txns, with one row for every label that appears in the table. A label no transaction carries produces no row. Rows come back in alphabetical order of type.
Example output — shape only; the figures below are invented, not this data's answer.
| type | num_txns |
|---|---|
| deposit | 9 |
| transfer | 3 |
| withdrawal | 12 |
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