On Apr 3, 2011, at 7:50 AM, Luuk wrote:
> On 03-04-2011 14:43, Colin Cuthbert wrote:
>> First time I've used this (or any!) mailing list, so sorry if I've done
>> something wrong.
>>
>> Pretty sure my question (in the subect) is phrased badly but it's the best I
>> could do!
>>
>> create table People(id integer primary key, name text);
>> insert into People (name) values ('bob');
>> insert into People (name) values ('fred');
>>
>> create table Cars(id integer primary key, name text);
>> insert into Cars (name) values ('ford');
>> insert into Cars (name) values ('volvo');
>>
>> create table CarOwners(id integer primary key, carId integer references
>> Cars(id), ownerId integer references People(id));
>> insert into CarOwners (carId, ownerId) select Cars.id, People.id from Cars,
>> People where Cars.name='ford' and People.name='bob';
>>
>> create table Couples(id integer primary key, personId1 integer references
>> People(id), personId2 integer references People(id));
>>
>> The last 'insert' statement seems to work for inserting a row into the
>> 'CarOwners' table, but I'm not sure that's the right/best way to do it.
>>
>> But how can I do a similar insert into the 'Couples' table? ie, how can I
>> insert a row (specifying 'personId1' and 'personId2' via queries based on
>> 'People.name') into the 'Couples' table?
>
> You forgot to define 'Couples'.....
>> Does it start something like this?
>>
>> insert into Couples (personId1, personId2) select id, id from People where...
>
> select id, id from People will return the same id (from the same record)
> twice....
>
> somehting like:
> select a.id, b.id from People a join People b on a.id<>b.id
> will give other results, but what youactually want to be returned
> depends on the definition of a 'Couple'...
>
You also want to do all of the above in a TRANSACTION, preferably with a
TRIGGER, to ensure the correct relationships are preserved.
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