SQL Server JOIN missing NULL values

Suppose I had the following 2 tables:

      Table1:                                Table2:
Col1:      Col2:     Col3:             Col1:       Col2:       Col4:
a          b         c                 a           b           d
e          <null>    f                 e           <null>      g
h          i         j                 h           i           k
l          <null>    m                 l           <null>      n
o          <null>    p                 o           <null>      q

Now, I want to join these tables on Col1 and Col2 and bring back the entire set to look like:

     Result:
Col1:      Col2:     Col3:     Col4:
a          b         c         d
e          <null>    f         g
h          i         j         k
l          <null>    m         n
o          <null>    p         q

So, I tried a SQL like:

SELECT Table1.Col1, Table1.Col2, Table1.Col3, Table2.Col4
FROM Table1 INNER JOIN Table2
ON Table1.Col1 = Table2.Col1 
AND Table1.Col2 = Table2.Col2

But it isn't matching the NULL values in Col2, so I end up with:

     Result:
Col1:      Col2:     Col3:     Col4:
a          b         c         d
h          i         j         k

How can I get the result I am looking for??

Thanks!

You can be explicit about the joins:

SELECT Table1.Col1, Table1.Col2, Table1.Col3, Table2.Col4
FROM Table1 INNER JOIN
     Table2
      ON (Table1.Col1 = Table2.Col1 or Table1.Col1 is NULL and Table2.Col1 is NULL) AND
         (Table1.Col2 = Table2.Col2 or Table1.Col2 is NULL and Table2.Col2 is NULL)

In practice, I would be more likely to use coalesce() in the join condition:

SELECT Table1.Col1, Table1.Col2, Table1.Col3, Table2.Col4
FROM Table1 INNER JOIN
     Table2
     ON (coalesce(Table1.Col1, '') = coalesce(Table2.Col1, '')) AND
        (coalesce(Table1.Col2, '') = coalesce(Table2.Col2, ''))

Where '' would be a value not in either of the tables.

Just a word of caution. In most databases, using any of these constructs prevents the use of indexes.

Use Left Outer Join instead of Inner Join to include rows with NULLS.

SELECT Table1.Col1, Table1.Col2, Table1.Col3, Table2.Col4
FROM Table1 LEFT OUTER JOIN 
    Table2 ON Table1.Col1 = Table2.Col1 
    AND Table1.Col2 = Table2.Col2

For more information, see here: http://technet.microsoft.com/en-us/library/ms190409(v=sql.105).aspx