> 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.
AFAIK, that's not true, i.e. subquery will be executed several times.
You can execute "select strftime('%s', 'now')" first and then put its
result into your query. But that won't work with view, of course.
Pavel
On Sun, Jul 22, 2012 at 11:17 AM, Kevin Martin <ke...@khn.org.uk> wrote:
> 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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> sqlite-users@sqlite.org
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