Shipments still missing a delivery timestamp

Question

A logistics control tower flags every dispatch that has left the warehouse but has no delivery confirmation yet. Undelivered parcels have a `NULL` value in `delivered_at`.

Return `dispatch_id`, `order_ref` and `courier_partner` for all dispatches that are **not yet delivered**.

Accepted Answer

Step 1: Identify the column that encodes the missing event — `delivered_at` is `NULL` until the parcel is signed for. Step 2: Filter with `delivered_at IS NULL`. This is the only correct test for missing values. Step 3: Do **not** write `delivered_at = NULL`. In SQL any comparison with `NULL` evaluates to unknown, so that predicate would return zero rows. Step 4: Project the three requested columns and you are done — no aggregation or joins needed.

Shipments still missing a delivery timestamp

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