Rewrite a NOT IN query safely
Replace a NULL-sensitive NOT IN pattern with a safer anti-join.
Find customers with no related support tickets even when tickets may contain NULL customer_id. Use an absence test whose comparison is scoped to each customer row. A single NULL in a NOT IN subquery can make every candidate comparison unknown. 1 Start from customers c The customer table is the population you want to preserve. 2 WHERE NOT EXISTS (SELECT 1 FROM tickets t WHERE t.customer_id = c.customer_id) For each customer, ask whether a matching ticket row exists. 3 Validate with a LEFT JOIN sample where t.customer_id IS NULL Spot-check that returned customers truly have no matching ticket. The anti-join…
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