>The other day i posted a rather lengthy message about a (self-induced)
>bug because i did not initialize a variable properly. The conclusion i
>get from the response to that post is that these are 'normal' constructs
>in firebird's stored procedure language :

...

> total = 0;
> select sum(...) form other_table into :total;

...

>Again, if i understood Ms Helen Borrie's message correctly, if the
>select returns NULL, the variable total will not be affected, so it will
>be still be zero.

>Today (at 5 AM, duh), i encountered another case with these lines :

...

> total = 0;
> select sum(detail.amount)
> from master
> join detail on (master_id = detail_id
> where (master.trans_date < :end_date) and
> (detail.item_id = :item_id)
> into :total;

...

>Since the tables are empty, the result of the variable TOTAL is always
>NULL inside this stored procedure (Firebird 1.5.3, Win32). This kinda
>contradicts my conclusion above (about how a SELECT INTO that returns a
>NULL will not affect the variable value).

>Just thought i'm gonna post this here before i went to bed :)
>Thank you all in advance,

I find this one an interesting issue also and I am wondering if there is
some

subtle difference between a query that includes an aggregate like sum and

a query that simply returns a field.

It seems like an aggregate might return a recordset containing one row of

data where the field may have a null value as in this example while a query
that

returns a field returns a null recordset with no records where there is no

matching data. Maybe the value of total is set to null because there is a

recordset returned by the query with a field containing null.

I might have this totally wrong, so hopefully an expert will be able to

clarify this.

Graeme Edwards









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