Category                        Items  
 Cat_Id(PK)        Cat_Name      Item_ID(PK)   Item_Name   Cat_Id(FK)
    1               abc             1            Item1         2
    2               Kar             2            Item2         1
    3               Isb             3            Item3         1
                                    4            Item4         3
                                    5            Item5         2 

SELECT Cat_Name,Cat_Id,CAST(0 AS int) AS Item_ID
FROM Category                        
UNION ALL
SELECT i.Item_Name,c.cat_ID,i.Item_ID
FROM Items i
INNER JOIN Category c
ON c.Cat_ID = i.Cat_ID
ORDER BY Cat_ID,Item_ID