The IFNULL function is unknown in Firebird. A look at the following list shows that the COALESCE function can be used instead in both Firebird and the internal HSQLDB. This function is even more universal because it can query any number of values and the first hit that is not NULL returns the corresponding value. Unfortunately, the base SQL editor does not provide the ability to share a term with Find and Replace. Otherwise IFNULL could simply be replaced by COALESCE if the term appears more frequently in a query. For such transformations, it is therefore advisable to copy the query into a simple text editor with search-and-replace function, then do the replacement and overwrite the old content with it.