Question

How in SQL could you “zip” together records in separate tables (à la the UNIX paste(1) utility)?

For example, assuming two tables, A and B, like so:

   A          B
========    ====
Harkness    unu
Costello    du
Sato        tri
Harper
Jones

How could you produce a single result set

   NAME  | NUM
===============
Harkness | unu
Costello | du
Sato     | tri
Harper   | NULL
Jones    | NULL

?

Answer 1

In SQL Server 2005, Oracle 9i and PostgreSQL 8.4 and higher:

SELECT  name, num
FROM    (
        SELECT  name, ROW_NUMBER() OVER (ORDER BY id) AS rn
        FROM    a
        ) qa
LEFT JOIN
        (
        SELECT  num, ROW_NUMBER() OVER (ORDER BY id) AS rn
        FROM    b
        ) qb
ON      qb.rn = qa.rn
ORDER BY
        qa.rn

Note that ROW_NUMBER() requires that the records are explicitly sorted.

If you don’t have a column similar to id, you cannot sort the records in order other than alphabetical, since relational databases have no concept of implicit record order.