Example 1
List orders whose customer does not exist
Orders 101 and 103 reference existing customers, so the joined customer row is present. Orders 102 and 104 point to customer ids 9 and 8, which are missing from customers, so the parent side is NULL and those orders are flagged as orphans.
Source table data Rows loaded before the example query runs.
Setup
CREATE TABLE customers (id INT, name VARCHAR(50));
CREATE TABLE orders (id INT, customer_id INT, total INT);
INSERT INTO
customers
VALUES
(1, 'Ada'),
(2, 'Bob');
INSERT INTO
orders
VALUES
(101, 1, 50),
(102, 9, 75),
(103, 2, 20),
(104, 8, 40);Validated query Shared across supported engines.
SQL
SELECT
o.id,
o.customer_id,
o.total
FROM
orders o
LEFT JOIN customers c ON c.id = o.customer_id
WHERE
c.id IS NULL
ORDER BY
o.id;Expected result Returned rows for the shared example.
| id | customer_id | total |
|---|---|---|
| 102 | 9 | 75 |
| 104 | 8 | 40 |
The child-to-parent audit uses the same `LEFT JOIN` and `IS NULL` pattern across engines.