Can you explain the difference between COALESCE and NULL?

In SQL, NULL represents the absence of a value. It is not a value itself; it indicates that the data is unknown or missing. COALESCE, on the other hand, is a function that takes a list of arguments and returns the first non‑NULL value among them. If all arguments are NULL, COALESCE returns NULL. For example, COALESCE(col1, col2, 'default') will return col1 if it is not NULL; otherwise it will return col2; if both are NULL, it returns 'default'. COALESCE is often used to provide fallback values or to replace NULLs with meaningful defaults. In contrast, NULL is simply a marker that a column has no value. Thus, COALESCE is a tool for handling NULLs, whereas NULL itself is the value that indicates missing data.