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Home/Questions/SQL/How would you handle nulls in a SQL join? Provide examples using COALESCE.

How would you handle nulls in a SQL join? Provide examples using COALESCE.

SQLmedium0.7 min readPremium

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Asked at these companies

Bristol Myers Squibb

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147 wordsInterview-ready

Nulls in SQL joins behave uniquely: NULL = NULL evaluates to NULL (not TRUE), so join keys with nulls typically don't match. Use COALESCE to normalize join keys. Example: SELECT * FROM orders o JOIN customers c ON COALESCE(o.customer_id, -1) = COALESCE(c.id, -1). For left joins where right-side columns may be null, use COALESCE in SELECT: COALESCE(c.name, 'Unknown Customer'). To include null-matching rows explicitly, use: ON (o.key = c.key OR (o.key IS NULL AND c.key IS NULL))....

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