diff --git a/calculate_largest_expensors.sql b/calculate_largest_expensors.sql
index e69de29..f763a90 100644
--- a/calculate_largest_expensors.sql
+++ b/calculate_largest_expensors.sql
@@ -0,0 +1,23 @@
+USE memory.default;
+
+-- NOTE: employee and expense tables must be created first
+-- Aggregate first, then join to minimise rows being joined
+-- Report employees who have expensed more than 1000 in total
+-- LEFT JOIN on manager to handle employees without a manager (e.g. CEO)
+SELECT
+    e.employee_id,
+    e.first_name || ' ' || e.last_name AS employee_name,
+    e.manager_id,
+    m.first_name || ' ' || m.last_name AS manager_name,
+    ex.total_expensed_amount
+FROM (
+    SELECT
+        employee_id,
+        SUM(unit_price * quantity) AS total_expensed_amount
+    FROM expense
+    GROUP BY employee_id
+    HAVING SUM(unit_price * quantity) > 1000
+) ex
+INNER JOIN employee e ON e.employee_id = ex.employee_id
+LEFT JOIN employee m ON m.employee_id = e.manager_id
+ORDER BY ex.total_expensed_amount DESC;
\ No newline at end of file
diff --git a/create_employees.sql b/create_employees.sql
index e69de29..620be23 100644
--- a/create_employees.sql
+++ b/create_employees.sql
@@ -0,0 +1,29 @@
+USE memory.default;
+
+-- Drop table if exists to allow re-running the script
+DROP TABLE IF EXISTS employee;
+
+-- Create the EMPLOYEE table based on hr/employee_index.csv
+-- employee_id and manager_id are TINYINT as per requirements
+CREATE TABLE employee
+(
+    employee_id TINYINT,
+    first_name VARCHAR,
+    last_name VARCHAR,
+    job_title VARCHAR,
+    manager_id TINYINT
+);
+
+-- Insert all employees from hr/employee_index.csv
+INSERT INTO employee
+VALUES
+    (1, 'Ian', 'James', 'CEO', 4),
+    (2, 'Umberto', 'Torrielli', 'CSO', 1),
+    (3, 'Alex', 'Jacobson', 'MD EMEA', 2),
+    (4, 'Darren', 'Poynton', 'CFO', 2),
+    (5, 'Tim', 'Beard', 'MD APAC', 2),
+    (6, 'Gemma', 'Dodd', 'COS', 1),
+    (7, 'Lisa', 'Platten', 'CHR', 6),
+    (8, 'Stefano', 'Camisaca', 'GM Activation', 2),
+    (9, 'Andrea', 'Ghibaudi', 'MD NAM', 2)
+;
\ No newline at end of file
diff --git a/create_expenses.sql b/create_expenses.sql
index e69de29..41ef6d7 100644
--- a/create_expenses.sql
+++ b/create_expenses.sql
@@ -0,0 +1,34 @@
+USE memory.default;
+
+-- NOTE: employee table must be created first (see create_employees.sql)
+
+-- Drop table if exists to allow re-running the script
+DROP TABLE IF EXISTS expense;
+
+-- Create the EXPENSE table
+CREATE TABLE expense (
+  employee_id TINYINT,
+  unit_price  DECIMAL(8, 2),
+  quantity    TINYINT
+);
+
+-- Insert expenses from finance/receipts_from_last_night
+-- Mapping employee names to IDs via INNER JOIN on employee table
+-- Expenses without a matching employee are excluded
+INSERT INTO expense
+SELECT 
+  e.employee_id,
+  r.unit_price,
+  r.quantity
+FROM (
+  VALUES
+    ('Alex Jacobson',     DECIMAL '6.50',   TINYINT '14'),
+    ('Alex Jacobson',     DECIMAL '11.00',  TINYINT '20'),
+    ('Alex Jacobson',     DECIMAL '22.00',  TINYINT '18'),
+    ('Alex Jacobson',     DECIMAL '13.00',  TINYINT '75'),
+    ('Andrea Ghibaudi',   DECIMAL '300.00', TINYINT '1'),
+    ('Darren Poynton',    DECIMAL '40.00',  TINYINT '9'),
+    ('Umberto Torrielli', DECIMAL '17.50',  TINYINT '4')
+) AS r(employee_name, unit_price, quantity)
+INNER JOIN employee e 
+  ON e.first_name || ' ' || e.last_name = r.employee_name;
\ No newline at end of file
diff --git a/create_invoices.sql b/create_invoices.sql
index e69de29..03816bb 100644
--- a/create_invoices.sql
+++ b/create_invoices.sql
@@ -0,0 +1,50 @@
+USE memory.default;
+
+DROP TABLE IF EXISTS invoice;
+DROP TABLE IF EXISTS supplier;
+DROP TABLE IF EXISTS invoices_raw;
+
+-- Raw invoice data exactly as in finance/invoices_due, no modifications
+CREATE TABLE invoices_raw (
+  company_name   VARCHAR,
+  invoice_amount DECIMAL(8, 2),
+  months_due     TINYINT
+);
+
+INSERT INTO invoices_raw VALUES
+  ('Catering Plus',         DECIMAL '2000.00', 2),
+  ('Catering Plus',         DECIMAL '1500.00', 3),
+  ('Dave''s Discos',        DECIMAL '500.00',  1),
+  ('Entertainment Tonight', DECIMAL '6000.00', 3),
+  ('Ice Ice Baby',          DECIMAL '4000.00', 6),
+  ('Party Animals',         DECIMAL '6000.00', 3);
+
+-- Create supplier table
+-- Deduplicate first, then apply RANK() for supplier_id
+CREATE TABLE supplier (
+  supplier_id TINYINT,
+  name        VARCHAR
+);
+
+INSERT INTO supplier
+SELECT
+  CAST(RANK() OVER (ORDER BY company_name asc) AS TINYINT) AS supplier_id,
+  company_name AS name
+FROM (SELECT DISTINCT company_name FROM invoices_raw);
+
+-- Create invoice table
+-- invoice_ammount is intentional typo from README spec
+CREATE TABLE invoice (
+  supplier_id     TINYINT,
+  invoice_ammount DECIMAL(8, 2),
+  due_date        DATE
+);
+
+INSERT INTO invoice
+SELECT
+  s.supplier_id,
+  r.invoice_amount,
+  date_trunc('month', current_date + r.months_due * interval '1' month)
+    + interval '1' month - interval '1' day AS due_date
+FROM invoices_raw r
+INNER JOIN supplier s ON s.name = r.company_name;
\ No newline at end of file
diff --git a/find_manager_cycles.sql b/find_manager_cycles.sql
index e69de29..27967f3 100644
--- a/find_manager_cycles.sql
+++ b/find_manager_cycles.sql
@@ -0,0 +1,35 @@
+USE memory.default;
+
+-- NOTE: employee table must be created first (see create_employees.sql)
+-- Find cycles in the manager approval hierarchy using recursive CTE
+-- A cycle exists when an employee appears as their own ancestor in the manager chain
+-- Results show each employee in a cycle and the full cycle chain as comma-separated employee_ids
+WITH RECURSIVE manager_chain(start_id, manager_id, chain, depth) AS (
+    -- Base case: start traversal from each employee
+    SELECT
+        employee_id AS start_id,
+        manager_id,
+        CAST(employee_id AS VARCHAR) AS chain,
+        1 AS depth
+    FROM employee
+
+    UNION ALL
+
+    -- Recursive case: follow manager chain upward
+    -- Stop if employee already appears in chain (cycle detected) or depth limit reached
+    SELECT
+        mc.start_id,
+        e.manager_id,
+        mc.chain || ',' || CAST(e.employee_id AS VARCHAR),
+        mc.depth + 1
+    FROM manager_chain mc
+    INNER JOIN employee e ON e.employee_id = mc.manager_id
+    WHERE mc.depth < 10
+      AND POSITION(CAST(e.employee_id AS VARCHAR) IN mc.chain) = 0
+)
+-- Return only employees where traversal loops back to the start
+SELECT
+    start_id AS employee_id,
+    chain
+FROM manager_chain
+WHERE manager_id = start_id;
\ No newline at end of file
diff --git a/generate_supplier_payment_plans.sql b/generate_supplier_payment_plans.sql
index e69de29..e1314b2 100644
--- a/generate_supplier_payment_plans.sql
+++ b/generate_supplier_payment_plans.sql
@@ -0,0 +1,55 @@
+USE memory.default;
+
+-- NOTE: invoice and supplier tables must be created first
+-- Generate monthly payment plan per supplier
+-- Step 1: explode each invoice into monthly payments
+--         floor rate for all months except last to avoid rounding errors
+--         last month rate = remainder to ensure exact total
+-- Step 2: group by supplier + payment_date to sum rates across multiple invoices
+-- Step 3: calculate balance_outstanding using window function
+WITH exploded AS (
+    SELECT
+        s.supplier_id,
+        s.name AS supplier_name,
+        i.invoice_ammount,
+        date_diff('month', date_trunc('month', current_date), i.due_date) AS months_due,
+        month_number,
+        date_trunc('month', current_date + month_number * interval '1' month)
+            + interval '1' month - interval '1' day AS payment_date,
+        CASE
+            -- All months except last: floor to avoid rounding up
+            WHEN month_number < date_diff('month', date_trunc('month', current_date), i.due_date)
+            THEN CAST(FLOOR(i.invoice_ammount / date_diff('month', date_trunc('month', current_date), i.due_date)) AS DECIMAL(8,2))
+            -- Last month: remainder to ensure invoice total is exact
+            ELSE i.invoice_ammount - CAST(FLOOR(i.invoice_ammount / date_diff('month', date_trunc('month', current_date), i.due_date)) AS DECIMAL(8,2))
+                 * (date_diff('month', date_trunc('month', current_date), i.due_date) - 1)
+        END AS monthly_rate
+    FROM invoice i
+    INNER JOIN supplier s ON s.supplier_id = i.supplier_id
+    CROSS JOIN UNNEST(SEQUENCE(1, date_diff('month', date_trunc('month', current_date), i.due_date))) AS t(month_number)
+),
+monthly AS (
+    -- Group by payment_date (not month_number) to correctly sum rates
+    -- across multiple invoices for the same supplier in the same month
+    SELECT
+        supplier_id,
+        supplier_name,
+        payment_date,
+        SUM(monthly_rate) AS payment_amount
+    FROM exploded
+    GROUP BY supplier_id, supplier_name, payment_date
+)
+SELECT
+    supplier_id,
+    supplier_name,
+    payment_amount,
+    -- Balance outstanding = total supplier amount minus cumulative payments so far
+    SUM(payment_amount) OVER (PARTITION BY supplier_id) -
+    SUM(payment_amount) OVER (
+        PARTITION BY supplier_id
+        ORDER BY payment_date
+        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
+    ) AS balance_outstanding,
+    payment_date
+FROM monthly
+ORDER BY supplier_id, payment_date;
\ No newline at end of file
diff --git a/tests.sql b/tests.sql
new file mode 100644
index 0000000..bb51563
--- /dev/null
+++ b/tests.sql
@@ -0,0 +1,175 @@
+USE memory.default;
+
+-- NOTE: all tables must be created first (see create_employees.sql, create_expenses.sql, create_invoices.sql)
+-- Data integrity and business logic tests
+-- Each test should return 0 rows if data is valid
+
+-- Test 1: Every expense must have a valid employee_id
+    SELECT 'FAIL: expense has invalid employee_id' AS test, COUNT(*) AS failures
+    FROM expense ex
+        LEFT JOIN employee e ON e.employee_id = ex.employee_id
+    WHERE e.employee_id IS NULL
+UNION ALL
+
+    -- Test 2: Every invoice must have a valid supplier_id
+    SELECT 'FAIL: invoice has invalid supplier_id' AS test, COUNT(*) AS failures
+    FROM invoice i
+        LEFT JOIN supplier s ON s.supplier_id = i.supplier_id
+    WHERE s.supplier_id IS NULL
+UNION ALL
+
+    -- Test 3: No NULL employee_id in employee table
+    SELECT 'FAIL: employee has NULL employee_id' AS test, COUNT(*) AS failures
+    FROM employee
+    WHERE employee_id IS NULL
+UNION ALL
+
+    -- Test 4: No NULL manager_id in employee table (except CEO)
+    SELECT 'FAIL: employee has NULL manager_id' AS test, COUNT(*) AS failures
+    FROM employee
+    WHERE manager_id IS NULL
+UNION ALL
+
+    -- Test 5: unit_price and quantity must be greater than 0
+    SELECT 'FAIL: expense has unit_price or quantity <= 0' AS test, COUNT(*) AS failures
+    FROM expense
+    WHERE unit_price <= 0 OR quantity <= 0
+UNION ALL
+
+    -- Test 6: invoice_ammount must be greater than 0
+    SELECT 'FAIL: invoice has invoice_ammount <= 0' AS test, COUNT(*) AS failures
+    FROM invoice
+    WHERE invoice_ammount <= 0
+UNION ALL
+
+    -- Test 7: due_date must be in the future
+    SELECT 'FAIL: invoice has due_date in the past' AS test, COUNT(*) AS failures
+    FROM invoice
+    WHERE due_date < current_date
+UNION ALL
+
+    -- Test 8: payment plan total must equal sum of invoices per supplier
+    SELECT 'FAIL: payment plan total does not match invoice total' AS test, COUNT(*) AS failures
+    FROM (
+    SELECT i.supplier_id
+        FROM (
+        SELECT supplier_id, SUM(invoice_ammount) AS total_invoiced
+            FROM invoice
+            GROUP BY supplier_id
+    ) i
+            JOIN (
+        WITH exploded AS  (
+            SELECT
+                s.supplier_id,
+                date_diff('month', date_trunc('month', current_date), i.due_date) AS months_due,
+                month_number,
+                CASE
+                    WHEN month_number < date_diff('month', date_trunc('month', current_date), i.due_date)
+                    THEN CAST(FLOOR(i.invoice_ammount / date_diff('month', date_trunc('month', current_date), i.due_date)) AS DECIMAL(8,2))
+                    ELSE i.invoice_ammount - CAST(FLOOR(i.invoice_ammount / date_diff('month', date_trunc('month', current_date), i.due_date)) AS DECIMAL(8,2))
+                         * (date_diff('month', date_trunc('month', current_date), i.due_date) - 1)
+                END AS monthly_rate
+            FROM invoice i
+                INNER JOIN supplier s ON s.supplier_id = i.supplier_id
+            CROSS JOIN UNNEST(SEQUENCE(1, date_diff('month', date_trunc('month', current_date), i.due_date))) AS t(month_number)
+        )
+SELECT supplier_id, SUM(monthly_rate) AS total_planned
+FROM exploded
+GROUP BY supplier_id
+) p ON i.supplier_id = p.supplier_id
+    WHERE ABS
+(i.total_invoiced - p.total_planned) > DECIMAL '0.01'
+)
+union all
+-- Test 9: last payment balance_outstanding must be 0 for each supplier
+SELECT 'FAIL: last payment balance is not 0 for some supplier' AS test, COUNT(*) AS failures
+FROM (
+    WITH exploded AS
+(
+        SELECT
+    s.supplier_id,
+    date_diff('month', date_trunc('month', current_date), i.due_date) AS months_due,
+    month_number,
+    date_trunc('month', current_date + month_number * interval '1'
+month)
+                + interval '1' month - interval '1' day AS payment_date,
+            CASE
+                WHEN month_number < date_diff
+('month', date_trunc
+('month', current_date), i.due_date)
+                THEN CAST
+(FLOOR
+(i.invoice_ammount / date_diff
+('month', date_trunc
+('month', current_date), i.due_date)) AS DECIMAL
+(8,2))
+                ELSE i.invoice_ammount - CAST
+(FLOOR
+(i.invoice_ammount / date_diff
+('month', date_trunc
+('month', current_date), i.due_date)) AS DECIMAL
+(8,2))
+                     *
+(date_diff
+('month', date_trunc
+('month', current_date), i.due_date) - 1)
+END AS monthly_rate
+        FROM invoice i
+        INNER JOIN supplier s ON s.supplier_id = i.supplier_id
+        CROSS JOIN UNNEST
+(SEQUENCE
+(1, date_diff
+('month', date_trunc
+('month', current_date), i.due_date))) AS t
+(month_number)
+    ),
+    monthly AS
+(
+        SELECT supplier_id, payment_date, SUM(monthly_rate) AS payment_amount
+FROM exploded
+GROUP BY supplier_id, payment_date
+    )
+,
+    plan AS
+(
+        SELECT
+    supplier_id,
+    payment_date,
+    SUM(payment_amount) OVER (PARTITION BY supplier_id) -
+            SUM(payment_amount) OVER (
+                PARTITION BY supplier_id
+                ORDER BY payment_date
+                ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
+            ) AS balance_outstanding,
+    ROW_NUMBER() OVER (PARTITION BY supplier_id ORDER BY payment_date DESC) AS rn
+FROM monthly
+    )
+SELECT supplier_id
+FROM plan
+WHERE rn = 1 AND balance_outstanding <> 0
+)
+UNION ALL
+
+-- Test 10: no negative payment amounts in payment plan
+SELECT 'FAIL: payment plan has negative payment_amount' AS test, COUNT(*) AS failures
+FROM (
+    WITH exploded AS
+(
+        SELECT
+    s.supplier_id,
+    date_diff('month', date_trunc('month', current_date), i.due_date) AS months_due,
+    month_number,
+    CASE
+                WHEN month_number < date_diff('month', date_trunc('month', current_date), i.due_date)
+                THEN CAST(FLOOR(i.invoice_ammount / date_diff('month', date_trunc('month', current_date), i.due_date)) AS DECIMAL(8,2))
+                ELSE i.invoice_ammount - CAST(FLOOR(i.invoice_ammount / date_diff('month', date_trunc('month', current_date), i.due_date)) AS DECIMAL(8,2))
+                     * (date_diff('month', date_trunc('month', current_date), i.due_date) - 1)
+            END AS monthly_rate
+FROM invoice i
+    INNER JOIN supplier s ON s.supplier_id = i.supplier_id
+        CROSS JOIN UNNEST(SEQUENCE(1, date_diff('month', date_trunc('month', current_date), i.due_date))) AS t(month_number)
+    )
+SELECT supplier_id
+FROM exploded
+WHERE monthly_rate < 0
+);
\ No newline at end of file