SELECT [Theme].[Name], [ThemeType].[Type]
FROM [Theme]
Left Outer Join [ThemeType] ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType]
ORDER BY CASE WHEN [ThemeType].[Type] IS NULL THEN 1 ELSE 0 END, [ThemeType].[Type]

SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme]
Left Outer Join [ThemeType] ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType]
WHERE [Theme].[ThemeTypeId] LIKE '%'
ORDER BY CASE WHEN [ThemeType].[Type] IS NULL THEN 1 ELSE 0 END, [ThemeType].[Type]

<asp:SqlDataSource ID="SqlDataSource6" runat="server"
    ConnectionString="<%$ ConnectionStrings:ApplicationServices %>"
    SelectCommand="SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme] Left Outer Join [ThemeType] ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType] ORDER BY CASE WHEN [ThemeType].[Type] IS NULL THEN 1 ELSE 0 END, [ThemeType].[Type]">
     <SelectParameters>
            <asp:QueryStringParameter Name="changeParam" Type="String" />
</SelectParameters>

SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme]
Left Outer Join [ThemeType]
             ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType]
WHERE COALESCE([Theme].[ThemeTypeId], 'null') LIKE '%'
ORDER BY CASE
         WHEN [ThemeType].[Type] IS NULL
         THEN 1
         ELSE 0
         END, [ThemeType].[Type]

SELECT
     [Theme].[Name],
     [ThemeType].[Type]
FROM
     [Theme] LEFT OUTER JOIN [ThemeType]
          ON
     [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType]
WHERE
     [Theme].[ThemeTypeId] = @changeParam
           OR
      (COALESCE([Theme].[ThemeTypeId], N'NULL') = N'NULL' AND @changeParam IS NULL)
ORDER BY
     CASE WHEN [ThemeType].[Type] IS NULL THEN 1 ELSE 0 END,
     [ThemeType].[Type]

DECLARE @t TABLE
(
    Theme       nvarchar(100),
    ThemeType   nvarchar(100)
)

INSERT INTO
    @t
    (
        Theme,
        ThemeType
    )
--I use the union since I am working on SQL Server 2005
SELECT
    N'1',
    N'1111'
UNION
SELECT
    N'1',
    N'----'
UNION
SELECT
    N'2',
    N'2222'
UNION
SELECT
    null,
    N'2222'

DECLARE @s  nvarchar(100)
SET @s = N'1' -- change this line for the criteria
--SET @s = null

SELECT
    *
FROM
    @t
WHERE
    Theme = @s
        OR
    (COALESCE(Theme, N'NULL') = N'NULL' AND @s IS NULL)

protected void viewThemeTypeAssociationsDropDown_OnSelectedIndexChanged(object sender, EventArgs e)
{
    if (viewThemeTypeAssociationsDropDown.SelectedIndex == 0)
    {
        SqlDataSource6.SelectCommand = "SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme] Left Outer Join [ThemeType] ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType] ORDER BY [Theme].[Name] ASC";
    }
    else if (viewThemeTypeAssociationsDropDown.SelectedIndex == 1)
    {
        SqlDataSource6.SelectCommand = "SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme], [ThemeType] WHERE [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType] ORDER BY [Theme].[Name] ASC";
    }
    else
    {
        SqlDataSource6.SelectCommand = "SELECT [Theme].[Name], [ThemeType].[Type] FROM [Theme] Left Outer Join [ThemeType] ON [Theme].[ThemeTypeId] = [ThemeType].[PK_ThemeType] WHERE [Theme].[ThemeTypeId] IS NULL ORDER BY [Theme].[Name] ASC";
    }
}