SELECT single row from child table for each row in parent table

Question

I am trying to get only one row from child table for each parent row with child fields included, I have been trying with GRUOP BY but with no success :( Here is my initial S

Answer 1

You didn't state your DBMS so this is a standard ANSI solution:

SELECT pID, lastname 
FROM parent 
  LEFT JOIN (
         SELECT pID, 
                row_number() over (partition by pid order by cid) as rn
         FROM child
         ) as child 
         ON parent.pID = child.pID and child.rn = 1

Which rows you define as the "first" row is up to you. There is no such as a "first" row unless you sort the rows - that's what the part order by cid does in the partition clause. So if you want something different as the "first" row, you need to change that.

Btw: there is no need to select all columns from the child table if you don't use them.