Question

Suppose I have three tables like this:

TABLE_X     TABLE_Y     TABLE_Z
---------------------------------------
2012/1/1    a           b
2012/1/2    a           b
...         a           b
2012/3/17   a           b
2012/3/18   a           b
2012/3/19   a           b
...         a           b
2012/12/22  a           b
2012/12/23  a           b
2012/12/24  a           b
...         a           b
2013/1/1    a           b

I need to do a view that uses GETDATE() as a condition. All values on and in the past of GETDATE() will take on TABLE_Y cols. All values in the future of GETDATE() will take on TABLE_Z cols.

view_TABLE_X_JOIN_Y_Z
---------------------
2012/1/1    a
2012/1/2    a
...         a
2012/3/17   a
2012/3/18   a
2012/3/19   a
...         a
2012/12/22  a
GETDATE()   a
2012/12/24  b
...         b
2013/1/1    b
2013/1/2    b

What I have tried:

SELECT x.Date
    ,CASE WHEN GETDATE() > x.Date THEN z.Value
    ELSE y.Value
    END AS Value
FROM TABLE_X x
LEFT JOIN TABLE_Y y ON x.Date = y.Date
LEFT JOIN TABLE_Z z ON x.Date = z.Date

The problem is that dates are not perfect FK references. i.e. Dates in TABLE_X is complete, but they are missing in some places in Y and Z.

Answer 1

You can use something like this:

SELECT 
  CASE WHEN table_x.date_column > GETDATE() THEN table_y.some_column 
                                            ELSE table_z.some_column END
FROM table_x JOIN table_y JOIN table_z (insert appropriate join clauses)