Flat tabel versus star schema

Hi,

I'm making some assumptions that I beleive meets your needs. You started with a query 
SELECT

    *
FROM Fact F
    JOIN Dim1 D1 ON F.d1key = D1.d1key
    JOIN Dim2 D2 ON F.d2key = D2.d2key
    JOIN Dim3 D3 ON F.d3key = D3.d3key
    JOIN Dim4 D4 ON F.d4key = D4.d4key
WHERE 'Some condition on say D2'

Now, to create a proper Star Model from this set AND keep all of your DIM tables small and relevant to the scope of the situation, just use the following:

SELECT
    F.*

FROM Fact F
    JOIN Dim2 D2 ON F.d2key = D2.d2key
WHERE 'Some condition on say D2'

SELECT DISTINCT
    D1.*

FROM Fact F
    JOIN Dim1 D1 ON F.d1key = D1.d1key
    JOIN Dim2 D2 ON F.d2key = D2.d2key
WHERE 'Some condition on say D2'

SELECT DISTINCT

    D2.*

FROM Fact F
    JOIN Dim2 D2 ON F.d2key = D2.d2key
WHERE 'Some condition on say D2'

SELECT DISTINCT

    D3.*

FROM Fact F
    JOIN Dim2 D2 ON F.d2key = D2.d2key
    JOIN Dim3 D3 ON F.d3key = D3.d3key
WHERE 'Some condition on say D2'

SELECT DISTINCT

    D4.*

FROM Fact F
    JOIN Dim2 D2 ON F.d2key = D2.d2key
WHERE 'Some condition on say D2'

Basically, the fact table keeps it all relevant, and you minimize joins to other tables for only what is needed in the where statement.

Instead of D1.*, maybe you only need 3 columns from D1 table. So replace that with the column names.

Maybe in order to get to D4, you have to do a join on D3 to get there. In this case, you'd have to keep D3 in the joins even though its not used in either the SELECT or WHERE statement. Also, if this is the case the original query looks different than the example I provided. 

Perhaps your WHERE statement has conditions on multiple tables. Then you need to maintain the joins in each dim table query to maintain the WHERE statement on those tables. 

In all cases it is extremely imporant to remember to include your relationship columns. If your JOIN is on 2 columns, then in both tables, you need to mesh them together into a single column somehow. I generally default to Col1|Col2. There are many ways to go about doing that, I recommned looking them up and using the method that works for you.

If this resolves your problem please let me know.