Q:

SQL: search for string set

In a table with user IDs and clothing items IDs there's a separate row for every item each user has. 
How can I sort out a group of users who has a specific list of clothing items? 
user_id item_id

1_cph   345 
10_brl  653 
5_cph   345 
2_brl   546 
1_cph   321 
1_cph   235 
1_cph   890 
1_cph   345 
2_brl   321 
2_brl   235 
2_brl   890 
2_brl   345 

Item ID search list:

321     
235     
890     

Question: Which users have all three items?     
Expected output
1_cph
2_brl       

A:

Try this
Select user_id -- take the user id
from yourtable
where item_id in ('id_item1', 'id_item2', 'id_item3') --that has these items
group by user_id --just 1 report entry per ID
having count(distinct item_id) >= 3 -- it has at least all the items listed

you could use having count(distinct item_id)> 2 to have people that has at least 2 of the 3 items searched

