Hi,
I have the following schema:
> CREATE TABLE aliases (name text not null, assignedTo text, validFrom integer
> not null);
> CREATE TABLE services (name text primary key, url text not null, type text
> not null);
> CREATE VIEW latest_aliases as select a.name, a.assignedTo, a.validFrom from
> aliases as a join (select name, max(validfrom) as mvf from aliases where
> validFrom <= strftime('%s', 'now') group by name) as b on a.name=b.name and
> a.validFrom=b.mvf;
> CREATE VIEW alias_info as select a.name, s.url, s.type from latest_aliases as
> a join services as s on a.assignedTo = s.name;
The aliases table maps names to services at different times. So for example
with the following data:
> sqlite> select * from services;
> svc1|http://somewhere|type1
> svc2|http://somewhere.else|type1
> sqlite> select *,datetime(validFrom, 'unixepoch') from aliases;
> env1|svc1|1342967110|2012-07-22 14:25:10
> env1|svc2|1342967185|2012-07-22 14:26:25
I want env1 to be mapped to svc1 after 14:25:10, until 14:26:25 after which
point I want it to be mapped to svc2.
This is done with the latest_aliases view, alias_info just joins latest_aliases
to the services table to get the connection info.
However, I'm quite concerned about executing strftime('%s', 'now') inside the
subquery, specifically does it execute multiple times? I don't want this to
happen because it could cause a rare bug when the list of services returned is
partly pre and partly post an update.
I'm trying to convince myself that the subquery in latest_aliases only executes
once, and also that alias_info only runs latest_aliases once. However, I'm not
doing very well at convincing myself. Can someone confirm this is true, or
suggest a nice solution to get the current time function out of the when clause.
Thanks,
Kevin Martin.
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