What are they and when to use them?

- IFNULL tests a column for the NULL value, returning the original value if it is NOT NULL and the second value we provide otherwise. The two columns need to be coercible to the same datatype. It's works like ISNULL in SQL Server.

- COALESCE works like IFNULL, but for multiple values. The first of them to return a non-null value is returned, otherwise resulting in a NULL.

- NULLIF allows you to replace a given value with a NULL, essentially saying "treat this value as it is was a missing value". An empty string, for example.

See below a representative example.

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