Missing IFNULL(), NULLIF(), COALESCE,
CASE and almost all standard SQL92 functions
My biggest complaint (besides too short keys and inability to
GROUP BY column_alias) is absence of almost all SQL functions.
In "core" InterBase there is no string and math functions at all
(all that is left are operators LIKE, CONTAINING, STARTING WITH,
|| and math arithmetic operators).
The standard solution to this problem is library of user
defined functions (UDF) written in C (on Whindows you can also use
Pascal). This is very similar to PostgreSQL's user-defined
functions but, unfortunately, overloading is not supported.
That would be end of story if UDF could deal with NULL values.
But they can't. Even worse, if you pass NULL as an argument
to UDF, the result is unpredictable because UDFs simply ignore
null indicator and grab argument value, which is just some
random garbage. In any case UDF cannot return NULL.
That leaves you pretty much in the dark if you need IFNULL(), or its generalized friend COALESCE().
