How can I select a table skipping duplicated value postgreSQL-CodePudding

I have a table like this.

id	grade_1	grade_2	createdAt
1	1	1	20220304
2	1	1	20220301
3	4	2	20220228

I want to select the current row(in here, id=1) and a row where the grade's value is different with the row I selected.(in here, id=3)

Like This

id	grade_1	grade_2	createdAt
1	1	1	20220304
3	4	2	20220228

I tried to use subquery but it doesn't really worked for me. Is there any way to skip the duplicated value when selecting table?

CodePudding user response：

You can just do it with group by and a max value to retieve the one you want

SELECT 
    grade_1, 
    grade_2, 
    Max(createdAt) 
from 
    yourTable
Group by 
    grade_1, 
    grade_2