合并两个Mysql表中的记录

Question

I have two tables:

records

id  subrecord_of
1   0
2   1
3   0
4   1
5   0
6   5

values

   id   value
    1   11
    1   111
    2   222
    2   222
    2   2222
    3   33
    4   44
    6   66
    6   666

The goal is to select records not being subrecords

with corresponding sum of values from records and subrecords:

id  sub    sum_of_values
1   2,4     11,111,2222,222,44
3   null    33
5   6       666,66

column "id" - records where sub is 0

column "sub" - list of subrecords fe id 2 and id 4 are subrecords of id 1

column "values" - list of unique values fe id 1 = distinct values from id1 + id2 + id4

Any help?

Answer 1

This is tricky, because the joins are going to generate a bunch of extra rows. The key idea for brining the data together is group_concat() and group by .

The following will work:

select r.id,
       group_concat(distinct rs.id) as sub,
       group_concat(distinct v.value) as values
from records r left join
     records rs
     on rs.subrecordof = r.id left join
     values v
     on v.id in (r.id, rs.id)
where r.subrecordof = 0
group by r.id;

Performance will not be particularly good. So, this solution should work well on smallish data sets. It might not work well on large data sets.