Question

I have data in below structure.

A
    A1 A2

    B  B1

    C  C1 C2 C3

These information transferred into two table named group1 and group2.

group1 has first level of data and middle level data.

group2 has last level of data and middle level data.

ie

group1

 group_name    group_id
  A             1
  A1            2
  B             3
  C             4
  C1            5
  C2            6

group2

 group2_name   parent_id
   A1             1
   A2             2
   B              1  
   B1             3
   C              1
   C1             4
   C2             5
   C3             6

Now i want to get the last level of information under the group A.

My output could be

group2_name
A2
B1
C3

I can fetch the information level 2 by using below query.

select group2.group_name from group2 
inner join
group1 on group1.group_id = group2.parent_id
where group1.group_name = 'A'

How can get the above output?

Here is SQLFIDDLE Demo

Kindly help me.

Answer 1

You could use this:

select
  group2.group_name
from
  group2 left join group1
  using(group_name)
where
  group1.group_name is null
  and group2.group_name like 'A%'    

that returns all elements from table group2 that are not present in table group1.
Or (depending on how your database is structured) also this:

select
  concat(left(group_name,1),
    case when max(mid(group_name,2,length(group_name)-1)+0)>0 then
              max(mid(group_name,2,length(group_name)-1)+0)
         else '' end)
from group2
where group2.group_name like 'A%'
group by left(group_name,1)

here I am grouping for the first character of the string, and getting the maximum value of the numeric value.