Weird SQL Server view definition

Question

I've "inherited" a well over 10-year old app, and it does show its age at times. I've stumbled across a really weird view definition today - I just can't seem to make sense of it! Can you help me? This was originally on SQL Server 7.0 and has since been migrated to SQL Server 2005 - but obviously it's never been refactored / redone....

This is the view definition - based on a bunch of tables and another view:

CREATE VIEW dbo.MyOddView
AS
SELECT     
    t1.MVOID, t1.SomeOtherColumn, 
    t2.Number , 
    t3.OID, t3.FKOID,
    t4.AcctNo, 
    t5.ShortDesc, t5.ZipCode, t5.City, 
    t6.BankAcctNo
FROM
    dbo.viewFirst vf
INNER JOIN
    dbo.Table1 t1 ON vf.MVOID = t1.MVOID AND vf.ValidFrom = t1.ValidFrom 
LEFT OUTER JOIN
    dbo.Table2 t2 
RIGHT OUTER JOIN
    dbo.Table3 t3 ON t2.OID = t3.FKOID 
LEFT OUTER JOIN
    dbo.Table4 t4 ON t3.ZVOID = t4.OID 
LEFT OUTER JOIN
    dbo.Table5 t5
INNER JOIN
    dbo.Table4 t6 ON t5.OID = t6.BCOID 
    ON t4.ZVOID = t5.OID 
    ON t2.AddressOID = t4.OID
GO

What I don't get are the two JOIN's (for Table2 t2 and Table5 t5) which have no JOIN condition listed next to them, and the two extra ON conditions at the end of the view definition - I can't seem to rip this apart and put it back together in "proper" ANSI JOIN syntax so that my row count is the same...... (my original view gets me something over 12'000 rows, and a first attempt at refactoring this returned a single row......)

Any ideas? What the heck is this? Seems like totally invalid SQL to me - but it appears to be doing its job (and has been for the past several years....) Any thoughts? Pointers?

Answer 1

SELECT ...
FROM   dbo.viewFirst vf
       INNER JOIN dbo.Table1 t1
         ON vf.MVOID = t1.MVOID
            AND vf.ValidFrom = t1.ValidFrom
       LEFT OUTER JOIN dbo.Table2 t2
                       RIGHT OUTER JOIN dbo.Table3 t3
                         ON t2.OID = t3.FKOID
                       LEFT OUTER JOIN dbo.Table4 t4
                         ON t3.ZVOID = t4.OID
                       LEFT OUTER JOIN dbo.Table5 t5
                                       INNER JOIN dbo.Table4 t6
                                         ON t5.OID = t6.BCOID
                         ON t4.ZVOID = t5.OID
         ON t2.AddressOID = t4.OID  

This syntax is covered in chapter 7 of Inside SQL Server 2008 T-SQL Querying or see this article by Itzik Ben Gan and the follow up letter by Lubor Kollar

Having the ON clause for t2.AddressOID = t4.OID last for example means that the JOIN of t2 logically happens last. i.e the other joins are logically processed first then the LEFT JOIN happens against the result of those Joins.