Some RDBMSs provide an ISNULL() function that can be used when dealing with potentially null values.

MySQL, MariaDB, and Oracle Database each have an ISNULL() function that returns 1 if its argument is null, and 0 if it’s not.

SQL Server also has an ISNULL() function, but it works differently. It works more like how the IFNULL() function works in some other RDBMSs.

Other RDBMSs, such as PostgreSQL and SQLite don’t include an ISNULL() function, but they do support the IS NULL predicate (as do the other RDBMSs).

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Some RDBMSs provide an IFNULL() function that can be used when dealing with potentially null values. In particular, MySQL, MariaDB, and SQLite each have an IFNULL() function that replaces any null values with another value.

Other RDBMSs, such as SQL Server, Oracle, and PostgreSQL provide similar functionality via functions of a different name.

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Most major RDBMSs support the NULLIF() operator, which returns NULL if both of its arguments are equivalent. If the arguments not equivalent, NULLIF() returns the first argument.

NULLIF() is a SQL-standard feature (it’s included in the ISO/IEC 9075 specification).

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