Complete SExI SQL take-home solution

.gitignore

@@ -0,0 +1,4 @@
+.venv/
+__pycache__/
+*.pyc
+.pytest_cache/

README.md

@@ -24,7 +24,9 @@ Let's get the repo forked and Trino installed. We can download a shiny new copy
 
 1. Fork this github repo.
 2. Download and install docker desktop. Instructions can be found [here](https://www.docker.com/products/docker-desktop/).
-3. Start the SExI container, by running `docker run --name=sexi-silverbullet -d trinodb/trino` at a terminal
+3. Start the SExI container, by running `docker run --name=sexi-silverbullet -p 8080:8080 -d trinodb/trino` at a 
+terminal. This publishes trino on `localhost:8080`, so you can connect to it from your own code later on. (If port 8080 
+is already taken on your machine, use something like `-p 8081:8080` instead.)
 4. You can reset the database at any time by running `docker restart sexi-silverbullet` at a terminal
 5. You can access a trino SQL shell using `docker exec -it sexi-silverbullet trino`. Here you can run any SQL commands 
 you like, as long as they're supported by trino.
@@ -136,9 +138,68 @@ the file is a valid SQL file.
 
 #
 
+Hold on. Before we ship any of this, Tim just asked me — with a straight face — how we know it's all correct. And, well. 
+He traded the last finance system for mince pies, so I'd rather not repeat that conversation. Let's prove our work.
+
+Don't worry, we don't need to test everything — just pick one thing and do it properly. Let's prove out the expenses 
+report, since that's the one the Chief of Staff is going to be reading.
+
+1. Write automated tests in Python that validate your `calculate_largest_expensors.sql` query. Please use `pytest` — 
+it's what we use here, and it keeps things consistent for whoever reviews your work.
+2. Put your tests in a `tests/` directory, along with a `tests/requirements.txt` and a line or two on how to run them. 
+The [`trino`](https://pypi.org/project/trino/) package gives you a client for talking to the database on 
+`localhost:8080`.
+
+Just the one query is plenty — we're far more interested in *how* you approach testing than in how much you cover. Some 
+things you might think about:
+- What counts as correct here? Consider the amounts, the ordering, and who does and doesn't show up in the results.
+- How does your test get the database into a known state before it asserts anything? `docker restart 
+sexi-silverbullet` resets everything, and your `create_*.sql` files will reload it.
+- If something is awkward to test because of the way the SQL is written, say so in your README. That's a useful 
+finding, not a failure.
+
+#
+
 Awesome! Finance will be so happy with us! Our tech guys are still rebuilding the production database, so upload your 
 code to github and take the rest of the afternoon off to ~~recover~~ relax!
 
 1. Upload all of your code to your forked github repo in a new branch, and create a pull request with your changes into 
-the main branch.
+the qa_test branch.
 2. Share your branch name with your recruiting contact, who will be in touch regarding the results of your test.
+
+## Solution
+
+Tested with Trino 483. `exployee_id` is treated as a typo because the CSV and
+reports use `employee_id`. `invoice_ammount` is kept because that exact name is
+part of the required schema.
+
+The loaders are repeatable. Invoice dates use Trino's `current_date`. The last
+payment absorbs the rounding remainder, so every invoice closes to the cent.
+The cycle report returns cycle members only, not employees who lead into one.
+
+Start Trino:
+
+```bash
+docker run --name=sexi-silverbullet -p 8080:8080 -d trinodb/trino:483
+```
+
+Load the data:
+
+```bash
+docker exec -i sexi-silverbullet trino < create_employees.sql
+docker exec -i sexi-silverbullet trino < create_expenses.sql
+docker exec -i sexi-silverbullet trino < create_invoices.sql
+```
+
+Run the reports:
+
+```bash
+docker exec -i sexi-silverbullet trino < calculate_largest_expensors.sql
+docker exec -i sexi-silverbullet trino < find_manager_cycles.sql
+docker exec -i sexi-silverbullet trino < generate_supplier_payment_plans.sql
+```
+
+The expense tests rebuild their two tables before each case. They verify the
+exact result, aggregation, the strict `> 1000` boundary, manager lookup, and
+stable ordering for equal totals.
+See [`tests/README.md`](tests/README.md) for the commands.

calculate_largest_expensors.sql

@@ -0,0 +1,22 @@
+WITH expense_total AS (
+    SELECT
+        employee_id,
+        SUM(unit_price * quantity) AS total_expensed_amount
+    FROM memory.default.expense
+    GROUP BY employee_id
+)
+SELECT
+    employee.employee_id,
+    employee.first_name || ' ' || employee.last_name AS employee_name,
+    employee.manager_id,
+    manager.first_name || ' ' || manager.last_name AS manager_name,
+    expense_total.total_expensed_amount
+FROM expense_total
+JOIN memory.default.employee AS employee
+    ON employee.employee_id = expense_total.employee_id
+JOIN memory.default.employee AS manager
+    ON manager.employee_id = employee.manager_id
+WHERE expense_total.total_expensed_amount > DECIMAL '1000.00'
+ORDER BY
+    expense_total.total_expensed_amount DESC,
+    employee.employee_id;

create_employees.sql

@@ -0,0 +1,22 @@
+DROP TABLE IF EXISTS memory.default.employee;
+
+CREATE TABLE memory.default.employee (
+    employee_id TINYINT,
+    first_name VARCHAR,
+    last_name VARCHAR,
+    job_title VARCHAR,
+    manager_id TINYINT
+);
+
+INSERT INTO memory.default.employee
+    (employee_id, first_name, last_name, job_title, manager_id)
+VALUES
+    (CAST(1 AS TINYINT), 'Ian', 'James', 'CEO', CAST(4 AS TINYINT)),
+    (CAST(2 AS TINYINT), 'Umberto', 'Torrielli', 'CSO', CAST(1 AS TINYINT)),
+    (CAST(3 AS TINYINT), 'Alex', 'Jacobson', 'MD EMEA', CAST(2 AS TINYINT)),
+    (CAST(4 AS TINYINT), 'Darren', 'Poynton', 'CFO', CAST(2 AS TINYINT)),
+    (CAST(5 AS TINYINT), 'Tim', 'Beard', 'MD APAC', CAST(2 AS TINYINT)),
+    (CAST(6 AS TINYINT), 'Gemma', 'Dodd', 'COS', CAST(1 AS TINYINT)),
+    (CAST(7 AS TINYINT), 'Lisa', 'Platten', 'CHR', CAST(6 AS TINYINT)),
+    (CAST(8 AS TINYINT), 'Stefano', 'Camisaca', 'GM Activation', CAST(2 AS TINYINT)),
+    (CAST(9 AS TINYINT), 'Andrea', 'Ghibaudi', 'MD NAM', CAST(2 AS TINYINT));

create_expenses.sql

@@ -0,0 +1,17 @@
+DROP TABLE IF EXISTS memory.default.expense;
+
+CREATE TABLE memory.default.expense (
+    employee_id TINYINT,
+    unit_price DECIMAL(8, 2),
+    quantity TINYINT
+);
+
+INSERT INTO memory.default.expense (employee_id, unit_price, quantity)
+VALUES
+    (CAST(3 AS TINYINT), DECIMAL '6.50', CAST(14 AS TINYINT)),
+    (CAST(3 AS TINYINT), DECIMAL '11.00', CAST(20 AS TINYINT)),
+    (CAST(3 AS TINYINT), DECIMAL '22.00', CAST(18 AS TINYINT)),
+    (CAST(3 AS TINYINT), DECIMAL '13.00', CAST(75 AS TINYINT)),
+    (CAST(9 AS TINYINT), DECIMAL '300.00', CAST(1 AS TINYINT)),
+    (CAST(4 AS TINYINT), DECIMAL '40.00', CAST(9 AS TINYINT)),
+    (CAST(2 AS TINYINT), DECIMAL '17.50', CAST(4 AS TINYINT));

create_invoices.sql

@@ -0,0 +1,37 @@
+DROP TABLE IF EXISTS memory.default.invoice;
+DROP TABLE IF EXISTS memory.default.supplier;
+
+CREATE TABLE memory.default.supplier (
+    supplier_id TINYINT,
+    name VARCHAR
+);
+
+-- IDs follow the alphabetical order of the source company names.
+INSERT INTO memory.default.supplier (supplier_id, name)
+VALUES
+    (CAST(1 AS TINYINT), 'Catering Plus'),
+    (CAST(2 AS TINYINT), 'Dave''s Discos'),
+    (CAST(3 AS TINYINT), 'Entertainment tonight'),
+    (CAST(4 AS TINYINT), 'Ice Ice Baby'),
+    (CAST(5 AS TINYINT), 'Party Animals');
+
+CREATE TABLE memory.default.invoice (
+    supplier_id TINYINT,
+    invoice_ammount DECIMAL(8, 2),
+    due_date DATE
+);
+
+INSERT INTO memory.default.invoice (supplier_id, invoice_ammount, due_date)
+VALUES
+    (CAST(5 AS TINYINT), DECIMAL '6000.00',
+        last_day_of_month(date_add('month', 3, current_date))),
+    (CAST(1 AS TINYINT), DECIMAL '2000.00',
+        last_day_of_month(date_add('month', 2, current_date))),
+    (CAST(1 AS TINYINT), DECIMAL '1500.00',
+        last_day_of_month(date_add('month', 3, current_date))),
+    (CAST(2 AS TINYINT), DECIMAL '500.00',
+        last_day_of_month(date_add('month', 1, current_date))),
+    (CAST(3 AS TINYINT), DECIMAL '6000.00',
+        last_day_of_month(date_add('month', 3, current_date))),
+    (CAST(4 AS TINYINT), DECIMAL '4000.00',
+        last_day_of_month(date_add('month', 6, current_date)));

find_manager_cycles.sql

@@ -0,0 +1,30 @@
+SET SESSION max_recursion_depth = 5;
+
+WITH RECURSIVE manager_path (
+    start_employee_id,
+    manager_id,
+    path
+) AS (
+    SELECT
+        employee_id,
+        manager_id,
+        ARRAY[employee_id]
+    FROM memory.default.employee
+
+    UNION ALL
+
+    SELECT
+        manager_path.start_employee_id,
+        manager.manager_id,
+        manager_path.path || manager.employee_id
+    FROM manager_path
+    JOIN memory.default.employee AS manager
+        ON manager.employee_id = manager_path.manager_id
+    WHERE NOT contains(manager_path.path, manager.employee_id)
+)
+SELECT
+    start_employee_id AS employee_id,
+    path || start_employee_id AS loop
+FROM manager_path
+WHERE manager_id = start_employee_id
+ORDER BY employee_id;

generate_supplier_payment_plans.sql

@@ -0,0 +1,73 @@
+WITH
+today AS (
+    SELECT date_trunc('month', current_date) AS month_start
+),
+invoice_terms AS (
+    SELECT
+        invoice.supplier_id,
+        invoice.invoice_ammount,
+        today.month_start,
+        date_diff(
+            'month',
+            today.month_start,
+            date_trunc('month', invoice.due_date)
+        ) AS months_to_pay
+    FROM memory.default.invoice AS invoice
+    CROSS JOIN today
+),
+invoice_payments AS (
+    SELECT
+        invoice_terms.supplier_id,
+        payment_no,
+        last_day_of_month(
+            date_add('month', payment_no, invoice_terms.month_start)
+        ) AS payment_date,
+        CASE
+            WHEN payment_no = invoice_terms.months_to_pay - 1 THEN
+                invoice_terms.invoice_ammount
+                - ROUND(
+                    invoice_terms.invoice_ammount
+                    / CAST(invoice_terms.months_to_pay AS DECIMAL(8, 0)),
+                    2
+                ) * CAST(invoice_terms.months_to_pay - 1 AS DECIMAL(8, 0))
+            ELSE ROUND(
+                invoice_terms.invoice_ammount
+                / CAST(invoice_terms.months_to_pay AS DECIMAL(8, 0)),
+                2
+            )
+        END AS payment_amount
+    FROM invoice_terms
+    CROSS JOIN UNNEST(
+        sequence(CAST(0 AS BIGINT), invoice_terms.months_to_pay - 1)
+    ) AS payment_numbers (payment_no)
+),
+monthly_supplier_payment AS (
+    SELECT
+        supplier_id,
+        payment_date,
+        SUM(payment_amount) AS payment_amount
+    FROM invoice_payments
+    GROUP BY supplier_id, payment_date
+)
+SELECT
+    monthly_supplier_payment.supplier_id,
+    supplier.name AS supplier_name,
+    CAST(monthly_supplier_payment.payment_amount AS DECIMAL(12, 2))
+        AS payment_amount,
+    CAST(
+        SUM(monthly_supplier_payment.payment_amount) OVER (
+            PARTITION BY monthly_supplier_payment.supplier_id
+        ) - SUM(monthly_supplier_payment.payment_amount) OVER (
+            PARTITION BY monthly_supplier_payment.supplier_id
+            ORDER BY monthly_supplier_payment.payment_date
+            ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
+        )
+        AS DECIMAL(12, 2)
+    ) AS balance_outstanding,
+    monthly_supplier_payment.payment_date
+FROM monthly_supplier_payment
+JOIN memory.default.supplier AS supplier
+    ON supplier.supplier_id = monthly_supplier_payment.supplier_id
+ORDER BY
+    monthly_supplier_payment.supplier_id,
+    monthly_supplier_payment.payment_date;

tests/README.md

@@ -0,0 +1,13 @@
+# Running the expense report tests
+
+Start Trino on `localhost:8080`, then create a virtual environment from the
+repository root:
+
+```bash
+python3 -m venv .venv
+.venv/bin/pip install -r tests/requirements.txt
+.venv/bin/pytest -q
+```
+
+The tests rebuild `EMPLOYEE` and `EXPENSE` before every case. Do not run them
+against a shared Trino memory catalogue.

tests/requirements.txt

@@ -0,0 +1,2 @@
+pytest==9.1.1
+trino==0.338.0

tests/test_largest_expensors.py

@@ -0,0 +1,83 @@
+from decimal import Decimal
+from pathlib import Path
+from typing import Iterator, cast
+
+import pytest
+import trino
+from trino.dbapi import Connection, Cursor
+
+
+ROOT = Path(__file__).resolve().parents[1]
+ReportRow = tuple[int, str, int, str, Decimal]
+Report = tuple[tuple[str, ...], list[ReportRow]]
+
+
+def execute_file(cursor: Cursor, filename: str) -> Cursor:
+    sql = (ROOT / filename).read_text(encoding="utf-8")
+    for statement in sql.rstrip(";\n").split(";"):
+        cursor.execute(statement.strip())
+    return cursor
+
+
+@pytest.fixture(scope="session")
+def trino_connection() -> Iterator[Connection]:
+    connection = trino.dbapi.connect(
+        host="localhost",
+        port=8080,
+        user="sexi_test",
+        catalog="memory",
+        schema="default",
+    )
+    yield connection
+    connection.close()
+
+
+@pytest.fixture()
+def expense_database(trino_connection: Connection) -> Cursor:
+    cursor = trino_connection.cursor()
+    execute_file(cursor, "create_employees.sql")
+    execute_file(cursor, "create_expenses.sql")
+    return cursor
+
+
+def read_report(cursor: Cursor) -> Report:
+    execute_file(cursor, "calculate_largest_expensors.sql")
+    rows = cast(list[ReportRow], [tuple(row) for row in cursor.fetchall()])
+    columns = tuple(column[0] for column in cursor.description)
+    return columns, rows
+
+
+def test_report_from_source_files(expense_database: Cursor) -> None:
+    columns, rows = read_report(expense_database)
+
+    assert columns == (
+        "employee_id",
+        "employee_name",
+        "manager_id",
+        "manager_name",
+        "total_expensed_amount",
+    )
+    assert rows == [
+        (3, "Alex Jacobson", 2, "Umberto Torrielli", Decimal("1682.00"))
+    ]
+
+
+def test_report_contract(expense_database: Cursor) -> None:
+    expense_database.execute(
+        """
+        INSERT INTO memory.default.expense VALUES
+            (CAST(2 AS TINYINT), DECIMAL '1930.00', CAST(1 AS TINYINT)),
+            (CAST(5 AS TINYINT), DECIMAL '500.00', CAST(2 AS TINYINT)),
+            (CAST(5 AS TINYINT), DECIMAL '111.11', CAST(1 AS TINYINT)),
+            (CAST(7 AS TINYINT), DECIMAL '1000.00', CAST(1 AS TINYINT)),
+            (CAST(8 AS TINYINT), DECIMAL '1111.11', CAST(1 AS TINYINT))
+        """
+    )
+
+    _, rows = read_report(expense_database)
+    assert rows == [
+        (2, "Umberto Torrielli", 1, "Ian James", Decimal("2000.00")),
+        (3, "Alex Jacobson", 2, "Umberto Torrielli", Decimal("1682.00")),
+        (5, "Tim Beard", 2, "Umberto Torrielli", Decimal("1111.11")),
+        (8, "Stefano Camisaca", 2, "Umberto Torrielli", Decimal("1111.11")),
+    ]