Question

I have a table EMPLOYEE with 100 people. I would like to write a query to find pairs of employees who have the same BIRTHDATE.

The result should return EMPNO, LASTNAME and BIRTHDATE for each employee in the pair (a 6-column result table).

I thought something like that

SELECT  t1.EmpNo
       ,t1.LastName
       ,t1.BirthDate
        ,t2.EmpNo
        ,t2.LastName
        ,t2.BirthDate
  FROM Employee t1
  INNER JOIN (
  SELECT EmpNo
        ,LastName
        ,BirthDate
  FROM Employee ) t2 ON t2.BirthDate = t1.BirthDate 
  WHERE t2.EmpNo != t1.EmpNo

Do you think it is correct?

Answer 1

I would just do:

SELECT t1.EmpNo, 
       t1.LastName, 
       t1.BirthDate, 
       t2.EmpNo, 
       t2.LastName, 
       t2.Birthdate
FROM Employee t1, Employee t2
WHERE t1.BirthDate = t2.Birthdate
AND t1.EmpNo <> t2.EmpNo