SQL: How to rewrite left join with unknown parameter in view - sql

Question

This is meant as kind of a simplified / more to the point question of:
NHibernate / QueryOver: How to left join with parameter
The core problem is that I have the following query:
1)
Select v.*, ...
from someView v
LEFT JOIN someTable t on v.ForeignKey = t.ForeignKey
AND t.SomeOtherValue = #myParam
where #myParam is some parameter.
I want to use this query inside a view but since I don´t know #myParam when creating the view I don´t know any way to attach it to the query so it is used directly inside the join. All I can do is get a version of the query like this:
2)
Select v.*, ...
from (someView v
LEFT JOIN someTable t ON v.ForeignKey = t.ForeignKey)
WHERE SomeOtherValue = 123
wich would in the view it would look like this:
3)
CREATE VIEW myView AS
Select v.*, t.SomeOtherValue, ...
from someView v
LEFT JOIN someTable t on v.ForeignKey = t.ForeignKey
and then say:
SELECT *
from myView
where SomeOtherValue = #myParam
In both cases (2 and 3) #myParam gets applied only after the left join already happened, so the result set is different (and in my case incorrect).
So I am searching for a way to rewrite 1) in a way so that I can use it inside a view (with similar syntax as in 2 and 3)
NOTE:
Using a table valued function with #myParam as parameter would work but then again I can´t use it as a model for NHibernate or with QueryOver, so that is not really an option.

Answer 1

On DB2, I accomplished what you're trying to do once by:
Making a scalar UDF function that was referenced in place of your #myParam.
The scalar UDF function retrieved the parameter value from a SESSION (temporary table).
Prior to referencing the view at runtime, my code created or recreated and populated the SESSION temporary table with a single row with the parameter value (giving the scalar UDF something to feed off of).
At runtime, the SQL view reference would call the scalar UDF function, which would access the temp table, and return the parameter value to the view, and voila, it worked.
On DB2, a table UDF function could perform in a similar manner. In general, table functions are more flexible than scalar functions, and are often a better choice.
DB2 supports late binding when using functions in that manner.
I don't know what database you're using, but you might have good luck trying something similar.