Question

I have a table, horribly designed (not my doing thankfully), that stores data in a fashion similar to the following:

[key], [lease_id], [building_name], ~20 more columns of data

A lease_id can and will exist for a centre as well as head office. I’ve been asked to find all instances where data in a building for a lease doesn’t match data in head office for the same lease.

I can do this, quite easily, with a self join. The challenge here is that there are about 20 columns to compare and although I could type each one in manually I was wondering if there’s a better way to do this (which would also mean the query can be used in future, accounting for any table changes).

In syntaxtically ridiculous psuedo code- I want to do something similar to what the following would do if it were to work:

select  lp.*
from    lease_proposal lp
        inner join
        (
            select  *
            from    lease_proposal lp2
            where   building_id = '001' -- assume 001 is head office for sake of example
        ) lp2
            on lp2.lease_id = lp.lease_id
where   lp.* <> lp2.*

Answer 1

You could do an INTERSECT operation to find all rows where all data matched, then LEFT JOIN that result and select only the rows where there wasn’t an intersection:

SELECT
    a.*
FROM
    lease_proposal a
LEFT JOIN
    (
        SELECT *
        FROM lease_proposal

        INTERSECT

        SELECT *
        FROM lease_proposal
        WHERE building_id = 001
    ) b ON a.lease_id = b.lease_id
WHERE
    b.lease_id IS NULL

If SQL Server supported it, you could also use a NATURAL LEFT JOIN like so:

SELECT  
    a.*
FROM
    lease_proposal a
NATURAL LEFT JOIN
    (
        SELECT *
        FROM lease_proposal
        WHERE building_id = 001
    ) b
WHERE b.lease_id IS NULL