🔥 SQL Interview Concept You MUST Know: COALESCE

COALESCE is one of the most useful SQL functions for handling missing (NULL) values in your data.

It returns the first non-NULL value from a list of expressions, making your queries cleaner and more reliable.

📌 Key points:

🔹 Replaces NULL values with meaningful defaults
🔹 Returns the first non-NULL expression
🔹 Improves report readability
🔹 Works with numbers, text, and dates
🔹 Prevents unexpected NULL results in calculations

💡 Common interview use cases:

✅ Replacing missing salaries with 0
✅ Displaying "Not Available" for NULL values
✅ Handling missing customer information
✅ Creating cleaner dashboards and reports
✅ Avoiding NULL values in calculations

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