join - Merge two rows in SQL

Question

Assuming I have a table containing the following information:

FK | Field1 | Field2
=====================
3  | ABC    | *NULL*
3  | *NULL* | DEF

is there a way I can perform a select on the table to get the following

FK | Field1 | Field2
=====================
3  | ABC    | DEF

Thanks

Edit: Fix field2 name for clarity

Answer 1

Aggregate functions may help you out here. Aggregate functions ignore NULLs (at least that's true on SQL Server, Oracle, and Jet/Access), so you could use a query like this (tested on SQL Server Express 2008 R2):

SELECT
    FK,
    MAX(Field1) AS Field1,
    MAX(Field2) AS Field2
FROM
    table1
GROUP BY
    FK;

I used MAX, but any aggregate which picks one value from among the GROUP BY rows should work.

Test data:

CREATE TABLE table1 (FK int, Field1 varchar(10), Field2 varchar(10));

INSERT INTO table1 VALUES (3, 'ABC', NULL);
INSERT INTO table1 VALUES (3, NULL, 'DEF');
INSERT INTO table1 VALUES (4, 'GHI', NULL);
INSERT INTO table1 VALUES (4, 'JKL', 'MNO');
INSERT INTO table1 VALUES (4, NULL, 'PQR');

Results:

FK  Field1  Field2
--  ------  ------
3   ABC     DEF
4   JKL     PQR