SELECT c.CategoryName, s.ID_Super
FROM Categories c
LEFT OUTER JOIN SuperCategories s ON c.ID_Category = s.SuperCategoryID

SELECT c.CategoryName, s.ID_Super
FROM Categories c
LEFT OUTER JOIN SuperCategories s ON c.ID_Category = s.SuperCategoryID

SELECT c.CategoryName, s.ID_Super
FROM Categories c
LEFT OUTER JOIN SuperCategories s ON c.ID_Category = s.SuperCategoryID

CategoryName    ID_Super
Box               1
Box               2
Red Box           NULL
Blue Box          3
Blue Plastic Box  NULL
Can               4
Tin Can           NULL

SELECT
     CAT.ID_Category,
     CAT.CategoryName
FROM
     Categories CAT
WHERE
     NOT EXISTS
     (
          SELECT
               *
          FROM
               SuperCategories SC
          WHERE
               SC.SuperCategoryID = CAT.ID_Category
     )

SELECT
     CAT.ID_Category,
     CAT.CategoryName
FROM
     Categories CAT
LEFT OUTER JOIN SuperCategories SC ON
     SC.SuperCategoryID = CAT.ID_Category
WHERE
     SC.ID_Super IS NULL

select CategoryName from Categories LEFT OUTER JOIN
SuperCategories ON Categories.ID_Category =SuperCategories.SuperCategoryID
WHERE SuperCategories.SuperCategoryID is  null

select CategoryName from Categories
where ID_Category not in (
    select SuperCategoryID
    from SuperCategories
)

SELECT
       isNull(a.[date_time],b.[date_time]) as [Time Stamp]
      ,isnull(a.[ip],b[ip]) as [Device Address]
      ,isnull(a.[total_messages],0) as [Local Messages]
      ,isnull(b.[total_messages],0) as [Remote Messages]
  FROM [Local_FW_Logs] a
FULL OUTER JOIN [Remote_FW_Logs] b
on b.ip = a.ip