I am trying to remove duplicate values ​​from rows based on a join on the same table, but cannot remove a value in a column in table1 that is mapped to the same column in table2.

date    | sid | comp | disc
-----------------------
23 june | 1  | az  | 20
23 june | 1  | ph  | 22
23 june | 1  | mg  | 10
23 june | 2  | mg  | 8
23 june | 3  | ph  | 15
23 june | 3  | az  | 11
------------------------

About self-joining

select t1.*, t2.comp as comp1, t2.disc as disc1
from table as t1
left join table as t2 on t1.date = t2.date and t1.sid = t2.sid and t1.comp <> t2.comp

Output from above query:

date    | sid | comp | disc | comp1 | disc1
-------------------------------------------
23 june | 1  | az  | 20     | ph    | 22
23 june | 1  | az  | 20     | mg    | 10
23 june | 1  | ph  | 22     | az    | 20
23 june | 1  | ph  | 20     | mg    | 10
23 june | 1  | mg  | 10     | mg    | 10
23 june | 2  | mg  | 10     | null  | null
23 june | 3  | ph  | 10     | az    | 11
23 june | 3  | az  | 11     | ph    | 10

Expected results: (Here I try to get a combination of comp and comp1 where for each sid and date there are only different comp values ​​mapped with mg and null in comp1 if the sid has only mg or non-mg values) NOTE: There will be no duplicate rows when comp is mapped to comp1

date    | sid | comp | disc | comp1 | disc1
-------------------------------------------
23 june | 1  | az  | 20     | mg    | 10
23 june | 1  | ph  | 20     | mg    | 10
23 june | 2  | mg  | 10     | null  | null
23 june | 3  | ph  | 10     | null  | null
23 june | 3  | az  | 11     | null  | null