Re: Triggers & Conditional Assignment

coalesce(NEW.end_date , OLD.end_date) will solve the issue.

On 9/15/05, Neil Saunders <n(dot)j(dot)saunders(at)gmail(dot)com> wrote:
>
> Hi,
>
> I've run in to a small problem when writing a trigger.
>
> For simplicities sake lets say that I have 2 tables – 'bookings' and
> 'unavailable_periods'. Both have columns 'start_date','end_date', and
> 'property_id'.
>
> I have written a trigger that is fired on inserts and updates for both
> tables that simply ensures that no intervals (defined by start_date
> and end_date) overlap for the same property across both tables.
>
> It works simply by doing a SELECT using the OVERLAP keyword on
> NEW.start_date, and NEW.end_date for both tables (Ignoring the record
> being modified). This works fine on inserts (Where both start_date and
> end_date are specified), and updates that modify both start_date and
> end_date, but for updates where I only update 'start_date', for
> example, the trigger fails because NEW.end_date is empty.
>
> Whats the best way around this?
>
> I've tried to write something along the lines of the following:
>
> DECLARE
> sdate DATE;
> edate DATE;
>
> BEGIN
> sdate = (NEW.start_date IS NOT NULL) ? NEW.start_date : OLD.start_date;
> edate = (NEW.end_date IS NOT NULL) ? NEW.end_date : OLD.end_date;
> …
>
> But conditional assignment doesn't seem to be catered for. The next
> best thing is a series of IF THEN ELSIF ELSE statements to assign
> sdate and edate, or is there another technique that I've missed
> entirely?
>
> Kind Regards,
>
> Neil Saunders.
>
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--
with regards,
S.Gnanavel
Satyam Computer Services Ltd.