SQL match column

Question

Let's assume I have this data. every person with id, has 2 coupon 1 and 2, which according to way to and back. Like this:

      ID     coupon from   to
"1000003328"    "1" "TSE"   "ALA"
"1000003328"    "2" "ALA"   "TSE"
"1000009615"    "1" "CIT"   "ALA"
"1000009615"    "2" "ALA"   "IST"
"1000014040"    "1" "DEL"   "ALA"
"1000014040"    "2" "ALA"   "FRU"
"1000017533"    "1" "KBP"   "ALA"
"1000017533"    "2" "ALA"   "PEK"
"1000020561"    "1" "ALA"   "CIT"
"1000020561"    "2" "CIT"   "ALA"
"1000026798"    "1" "GUW"   "SCO"
"1000026798"    "2" "SCO"   "GUW"

Is it possible to extract only men, where data from row 1 from column "from" coupon 1 match with row2 from column "to" coupon 2 ? This one fits to the abovementioned condititon:

       ID     coupon from   to
"1000003328"    "1"  "TSE"   "ALA"
"1000003328"    "2"  "ALA"   "TSE" 

because of row 1 column "from" coupon 1 (TSE) equal to row2 column "to" coupon 2.

Thank u!

Answer 1

With EXISTS :

select t.* from tablename t
where exists (
  select 1 from tablename
  where id = t.id and coupon <> t.coupon and "from" = t."to" and "to" = t."from"
)

If there is never a case of from to be equal to to then you can remove the condition and coupon <> t.coupon .
See the demo .
Results:

| id         | coupon | from | to  |
| ---------- | ------ | ---- | --- |
| 1000003328 | 1      | TSE  | ALA |
| 1000003328 | 2      | ALA  | TSE |
| 1000020561 | 1      | ALA  | CIT |
| 1000020561 | 2      | CIT  | ALA |
| 1000026798 | 1      | GUW  | SCO |
| 1000026798 | 2      | SCO  | GUW |

Answer 2

You specifically reference coupons "1" and "2", so I would go for:

select t.*
from t
where t.coupon in (1, 2) and
      exists (select 1
              from t t2
              where t2.id = t.id and
                    t2.from = t.to and
                    t2.to = t.from and
                    t2.coupon <> t.coupon
             );

Note that to and from are very poor choices for column names because they are SQL keywords.