sql query to compare values row wise? - mysql

Question

i have a table which contains some data as an example:
+----------+-----+------+
| order_id | poi | povi |
+----------+-----+------+
| 1 | A | a |
| 1 | B | b |
| 1 | C | c |
| 2 | A | a |
| 2 | B | b |
| 2 | C | c |
| 3 | A | a |
| 3 | B | b |
| 4 | C | c |
| 5 | A | a |
| 5 | B | b |
| 6 | C | c |
| 7 | A | a |
| 8 | B | b |
| 9 | C | c |
+----------+-----+------+
i have 3 set of values of poi and povi like {A,a},{B,b},{C,c}
i want to get the order_id which contains all three of them, like in the above case the output should be.(order_id which have poi and povi as {A,a} and {B,b} and {C,c} but the problem is that they are diffrent rows)
+----------+
| order_id |
+----------+
| 1 |
| 2 |
+----------+
any idea?

Answer 1

So many times people just getting started ask similar questions to those already asked and answered, including this common scenario. However, not being able to apply know answers to your scenario doesn't help you wrap your head around what is asked, or how the query works in their own scenario... That said, lets look at yours.
You want all DISTINCT orders that have ALL of the following A/a, B/b, C/c entries. Multiple ways to resolve, but the most common is with a where / group by / having.
Start with something simple, looking for any order that has A/a
select
yt.Order_id
from
YourTable yt
where
( yt.poi = 'A' AND yt.poiv = 'a' )
and you would get order 1, 2, 3, 5 and 7. That is simple...
Now, add in your other criteria
select
yt.Order_id
from
YourTable yt
where
( yt.poi = 'A' AND yt.poiv = 'a' )
OR ( yt.poi = 'B' AND yt.poiv = 'b' )
OR ( yt.poi = 'C' AND yt.poiv = 'c' )
and this will give you all rows, but not what you want, but you should be able to see the where criteria is checking for both parts of POI / POIV with an OR between each possible combination. You obviously can not have one record that has a POI of both "A" and "B", that is why the "OR" between each paired ( AND ) criteria. But again, this gives ALL rows. But it is also qualifying only the pieces. So lets add one next step... a group by via the order, but HAVING clause expecting 3 records...
select
ytA.Order_id
from
YourTable ytA
where
( yt.poi = 'A' AND yt.poiv = 'a' )
OR ( yt.poi = 'B' AND yt.poiv = 'b' )
OR ( yt.poi = 'C' AND yt.poiv = 'c' )
group by
yt.Order_id
HAVING
count(*) = 3
The count(*) is to count how many records qualified the WHERE clause and will only return those records that had 3 entries.
Now, what if someone has multiple orders of A/a, A/a, B/b... This COULD give a false answer returned value, but please confirm these queries to meet your needs.
Although accepted, here is another way I would have written the query... somewhat similar to another post below. The premise of this version of the query is to utilize an index and qualify at least 1 record found before trying to find ALL. In this case, it first qualifies for those with an A/a. If an order does not have that, it does not care about looking for a B/b, C/c. If it DOES, then the join qualifies to the next levels too
select
ytA.Order_id
from
YourTable ytA
JOIN YourTable ytB
on ytA.Order_id = ytB.Order_id
AND ytB.poi = 'B'
AND ytB.poiv = 'b'
JOIN YourTable ytC
on ytB.Order_id = ytC.Order_id
AND ytC.poi = 'C'
AND ytC.poiv = 'c'
where
ytA.poi = 'A'
AND ytA.poiv = 'a'

Answer 2

find the "intersection" of lists, each of which contains one set
select id
from
(select id from mytable where poi = 'A' and povi= 'a') t1
inner join
(select id from mytable where poi = 'B' and povi= 'b') t2
using(id)
inner join
(select id from mytable where poi = 'C' and povi= 'c') t3
using(id)
demo