If you are calling stored procedure then in the procedure I'd do it like this:

IF @parameter IS NULL -- assuming that you pass NULL when ALL is selected

BEGIN;

SELECT * FROM TABLE;

END;

ELSE

BEGIN;

SELECT * FROM TABLE WHERE COLUMN = @parameter;

END;

If you are not calling a stored procedure but have embedded sql I'd do something like this in the dataset:

="SELECT * FROM Table " & IIf(! ISNOTHING(Parameters!ReportParameter1.Value), "WHERE Column = " & Parameters!ReportParameter1.Value, "" )" (