Re: UNION or LEFT JOIN?

Louis-David,

Please advice me,

if some cabin doesn't have a price i.e. it is not available, is there some
way to tell
which cruise it belongs to?

You have PRICE table which seems to me to be an associative table between
cruise and cabin, is this correct?

But, if the price doesn't have a register for that pair
(îd_cabin,id_cruise), how do you know that cabin belongs to that cruise, in
this case, cruise nº 1?

Best,
Oliveiros

2010/2/16 Louis-David Mitterrand
<vindex+lists-pgsql-sql(at)apartia(dot)org<vindex%2Blists-pgsql-sql(at)apartia(dot)org>
>

> Here is the basic schema:
>
> -------------------------->id_ship>-----------------------
> | |
> [SHIP]->id_ship->[CABIN]->id_cabin->[PRICE]<-id_cruise<-[CRUISE]
>
> It's a database of cruise prices.
>
> Each 'price' object has a reference to 'cabin' and 'cruise'
>
> 'cabin' belongs to a 'ship', so does 'cruise'
>
> I'm trying to select all cabins of cruise N°1 with prices OR nothing if
> there is no price (meaning cabin not available). I want all cabins
> listed, price or no price.
>
> Also when doing the query I don't have the id_ship, only the id_cruise.
>
> What is the best way of doing it? UNION or LEFT JOIN? I tried the latter
> without success and am unsure on how do do the former.
>
> Thanks,
>
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