Select first record in a One-to-Many relation using left join

Question

I\'m trying to join two tables using a left-join. And the result set has to include only the first record from the \"right\" joined table.

Lets say I have two tables

Answer 1

If you are on SQL Server 2005 or later version, you could use ranking to achieve what you want. In particular, ROW_NUMBER() seems to suit your needs nicely:

WITH B_ranked AS (
  SELECT
    *,
    rnk = ROW_NUMBER() OVER (PARTITION BY code ORDER BY city)
  FROM B
)
SELECT
  A.code,
  A.emp_no,
  B.city,
  B.county
FROM A
  LEFT JOIN B_ranked AS B ON A.code = B.code AND b.rnk = 1

OR

WITH B_unique_code AS (
  select * from(
     SELECT
      *,
      rnk = ROW_NUMBER() OVER (PARTITION BY code ORDER BY city)
      FROM B
     ) AS s
  where rnk = 1
)
SELECT
  A.code,
  A.emp_no,
  B.city,
  B.county
FROM A
  LEFT JOIN B_unique_code AS B ON A.code = B.code