Default column and rows in matrix
When you’d like to display some columns and rows in a matrix, even though there is no actual data for them, the solution is to add them to the dataset before its processed into the matrix. An easy way to do this is to alter the dataset for the matrix. Use a temporary table and insert the default values into it, then insert the actual data into it et voila:
becomes:
As you can see, the second matrix contains a lot more rows 
! Of course it displays NULL in most cases, but you can easily change NULL into anything else using this expression in the data field:
=IIF(Fields!MatrixData.value IS NOTHING, 0, Fields!MatrixData.value)
The SQL query I used to create a matrix with some default values:
DECLARE @TempTable TABLE
(
EyeColor NVARCHAR(50),
City NVARCHAR(50),
COUNTNames INT
)
INSERT INTO @TempTable
SELECT EyeColor, City, COUNT(Name) FROM Person GROUP BY EyeColor, City
INSERT INTO @TempTable
VALUES ('Brown', 'Amsterdam', NULL)
INSERT INTO @TempTable
VALUES ('Blue', 'New York', NULL)
INSERT INTO @TempTable
VALUES ('Green', 'London', NULL)
INSERT INTO @TempTable
VALUES ('Grey', 'Miami', NULL)
SELECT EyeColor, City, SUM(COUNTNames) AS COUNTNames FROM @TempTable GROUP BY EyeColor, City
As you can see, I used a temporary table. In my case a variable table was suitable, but a table in the TempDB using a CREATE TABLE #TempTable statement is also a solution. The table attributes need to correspond with the attributes in the actual dataset.
Fill the table with the actual data and then with the default values you’d like to see in your columns and rows.