Efficient way to join two tables with one to many relationship

This is interview question asked to me in interview and i was not able to answer. Please help..

What is the most efficient way to join two table with one to many relationship between them

Most effective way is to use an INNER JOIN, like this:

SELECT   *
FROM        Parent P
INNER JOIN  Child  C
    ON      C.ParentId = P.ParentId

And when you need aggregates on child level, you can add a GROUP BY and SUM and/or AVG or other aggregate functions:

SELECT      P.Name
            , P.Address
            , SUM(C.Amount)
FROM        Parent P
INNER JOIN  Child  C
    ON      C.ParentId = P.ParentId
GROUP BY    P.Name
            , P.Address

StackExchange Database Administrators Q#118693, answer score: 9