Question

I have a table containing many columns, I have to make my selection according to these two columns:

TIME   ID
-216   AZA
 215   AZA
  56   EA
 -55   EA
  66   EA
 -03   AR
  03   OUI
-999   OP
 999   OP
  04   AR
  87   AR

The expected output is

 TIME   ID
  66   EA
  03   OUI
  87   AR

I need to select the rows with no matches. There are rows which have the same ID, and almost the same time but inversed with a little difference. For example the first row with the TIME -216 matches the second record with time 215. I tried to solve it in many ways, but everytime I find myself lost.

Answer 1

First step — find rows with duplicate IDs. Second step — filter for rows which are near-inverse duplicates.

First step:

SELECT t1.TIME, t2.TIME, t1.ID FROM mytable t1 JOIN mytable
 t2 ON t1.ID = t2.ID AND t1.TIME > t2.TIME;

The second part of the join clause ensures we only get one record for each pair.

Second step:

SELECT t1.TIME,t2.TIME,t1.ID FROM mytable t1 JOIN mytable t2 ON t1.ID = t2.ID AND
 t1.TIME > t2.TIME WHERE ABS(t1.TIME + t2.TIME) < 3;

This will produce some duplicate results if eg. (10, FI), (-10, FI) and (11, FI) are in your table as there are two valid pairs. You can possibly filter these out as follows:

 SELECT t1.TIME,MAX(t2.TIME),t1.ID FROM mytable t1 JOIN mytable t2 ON
 t1.ID = t2.ID AND t1.TIME > t2.TIME WHERE ABS(t1.TIME + t2.TIME) < 3 GROUP BY 
 t1.TIME,t1.ID;

But it’s unclear which result you want to drop. Hopefully this points you in the right direction, though!