Hi there,

according to the SQL92 standard:

===
Set Function Specification

... bla bla bla ...


<set function type> ::=
AVG | MAX | MIN | SUM | COUNT

... bla bla bla ...

General Rules

1) Case:

a) If COUNT(*) is specified, then the result is the cardinality
of T.

b) Otherwise, let TX be the single-column table that is the
result of applying the <value expression> to each row of T
and eliminating null values. If one or more null values are
eliminated, then a completion condition is raised: warning-
null value eliminated in set function.

... bla bla bla ...

b) If AVG, MAX, MIN, or SUM is specified, then

Case:

i) If TXA is empty, then the result is the null value.
===

Where, I believe, TXA is the resultset -> hence, the NULL result. No
resultset, the function returns 'NULL'.

And that is why SUM(no result) returns NULL


Martijn Tonies
InterBase Workbench - the developer tool for InterBase and Firebird
http://www.interbaseworkbench.com



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