Finding the id's which include multiple criteria in long format - sql

Question

Suppose I have a table like this,
id
tagId
1
1
1
2
1
5
2
1
2
5
3
2
3
4
3
5
3
8
I want to select id's where tagId includes both 2 and 5. For this fake data set, It should return 1 and 3.
I tried,
select id from [dbo].[mytable] where tagId IN(2,5)
But it takes 2 and 5 into account respectively. I also did not want to keep my table in wide format since tagId is dynamic. It can reach any number of columns. I also considered filtering with two different queries to find (somehow) the intersection. However since I may search more than two values inside the tagId in real life, it sounds inefficient to me.
I am sure that this is something faced before when tag searching. What do you suggest? Changing table format?

Answer 1

One option is to count the number of distinct tagIds (from the ones you're looking for) each id has:
SELECT id
FROM [dbo].[mytable]
WHERE tagId IN (2,5)
GROUP BY id
HAVING COUNT(DISTINCT tagId) = 2

Answer 2

This is actually a Relational Division With Remainder question.
First, you have to place your input into proper table format. I suggest you use a Table Valued Parameter if executing from client code. You can also use a temp table or table variable.
DECLARE #ids TABLE (tagId int PRIMARY KEY);
INSERT #ids VALUES (2), (5);
There are a number of different solutions to this type of question.
Classic double-negative EXISTS
SELECT DISTINCT
mt.Id
FROM mytable mt
WHERE NOT EXISTS (SELECT 1
FROM #ids i
WHERE NOT EXISTS (SELECT 1
FROM mytable mt2
WHERE mt2.id = mt.id
AND mt2.tagId = i.tagId)
);
This is not usually efficient though
Comparing to the total number of IDs to match
SELECT mt.id
FROM mytable mt
JOIN #ids i ON i.tagId = mt.tagId
GROUP BY mt.id
HAVING COUNT(*) = (SELECT COUNT(*) FROM #ids);
This is much more efficient. You can also do this using a window function, it may be more or less efficient, YMMV.
SELECT mt.Id
FROM mytable mt
JOIN (
SELECT *,
total = COUNT(*) OVER ()
FROM #ids i
) i ON i.tagId = mt.tagId
GROUP BY mt.id
HAVING COUNT(*) = MIN(i.total);
Another solution involves cross-joining everything and checking how many matches there are using conditional aggregation
SELECT mt.id
FROM (
SELECT
mt.id,
mt.tagId,
matches = SUM(CASE WHEN i.tagId = mt.tagId THEN 1 END),
total = COUNT(*)
FROM mytable mt
CROSS JOIN #ids i
GROUP BY
mt.id,
mt.tagId
) mt
GROUP BY mt.id
HAVING SUM(matches) = MIN(total)
AND MIN(matches) >= 0;
db<>fiddle
There are other solutions also, see High Performance Relational Division in SQL Server