If the value of <expr1> is not NULL, returns <expr1>; otherwise, returns <expr2>.
IFNULL(<expr1>, <expr2>)
<expr1>: The expression to be checked for NULL.<expr2>: The value to return if <expr1> is NULL.<expr1> is not NULL, returns <expr1>.<expr2>.SELECT IFNULL(1, 0);
+--------------+ | IFNULL(1, 0) | +--------------+ | 1 | +--------------+
SELECT IFNULL(NULL, 10);
+------------------+ | IFNULL(NULL, 10) | +------------------+ | 10 | +------------------+
SELECT IFNULL(NULL, NULL);
+--------------------+ | IFNULL(NULL, NULL) | +--------------------+ | NULL | +--------------------+