customer_changes is a change-data-capture feed from the customer database: one row per change, with columns lsn, customer_id, op, email, city, changed_at.
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op is 'I' (insert), 'U' (update) or 'D' (delete). - •
I and U rows carry the full row after the change; D rows carry NULL email and city. - •
lsn is the database's log sequence number — the order the changes were committed. changed_at comes from application servers whose clocks aren't synchronised.
Return the table as it stands after applying every change in commit order: one row per customer that still exists.
Columns: customer_id, email, city. Sort by customer_id.