如何用一个SQL检查多个记录之间的列值是否相同

Question

suppose there is a table

id      desc
1        a
1        b
1        c
1        a
2        a
2        a

what I want to do is to show a mix of desc if the desc under the same id are different, otherswise show the value of the desc. Just like below

id     desc
1      a/b/c
2      a

How could I do it in one sql ?

enter code here

Answer 1

I think you want group_concat() with the distinct modifier:

select id, group_concat(distinct `desc` separator '/') as `desc`
from t
group by id;

Note that desc is a bad name for a column because it is a SQL keyword (think order by ). It is best to avoid grammatical elements when choosing names.