Re: Select rows when all all ids of its children records matches

> On 12 Sep 2018, at 17:44, Arup Rakshit <ar(at)zeit(dot)io> wrote:
>
> Can you show me the SQL construction? Do I need to use `WITH`?

An option is to create a bit-wise OR and SUM the grouped results. If the result of these 3 bits is 7, than the post matches all three tags.

select p.id, p.name
from post p
join post_tag pt on (pt.post = p.id)
join tag t on (t.id = pt.tag)
where t.id in (1, 2, 3)
group by
case t.id
when 1 then 1
when 2 then 2
when 3 then 4
else 0
end
having sum(case t.id
when 1 then 1
when 2 then 2
when 3 then 4
else 0
end) = 7;

I used ints here for the bitwise OR, a bitstring would probably be neater.

Another approach is to aggregate the set of matching tags into an array using array_agg(). I think that's what David means. You could then check the length of the array to see if you have all 3 (or 4 or 5 or 9000).

>> On 12-Sep-2018, at 9:13 PM, David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>>
>> On Wednesday, September 12, 2018, Arup Rakshit <ar(at)zeit(dot)io> wrote:
>> IN is OR, I want the AND logic. Select posts which has tag 1, 2 and 3 ( tag ids )
>>
>> Build arrays and then use the “contains” operator.
>>
>> David J.
>

Alban Hertroys
--
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cut the trees and you'll find there is no forest.