Question

I have a simple table :

DECLARE @t TABLE(item INT, itemType INT  )

insert INTO @t SELECT 1000,0
insert INTO @t SELECT 1000,3
insert INTO @t SELECT 1000,5
insert INTO @t SELECT 1000,6
insert INTO @t SELECT 2000,0
insert INTO @t SELECT 2000,3
insert INTO @t SELECT 2000,5
insert INTO @t SELECT 2000,6
insert INTO @t SELECT 3000,0
insert INTO @t SELECT 3000,10
insert INTO @t SELECT 4000,11

I want to select all items where itemtype = 3 but if there is a row , provide also its base itemtype (if it exists) which is itemType = 0.

For example :

• for itemType = 3

  1000,0 should be provided –why ? because table also has 1000 + itemType 0
  1000,3 should be provided –why ? because we looked for itemType=3
  2000,0 should be provided –why ? because table has found 2000,3 and this 2000 also has itemType=0
  2000,3 should be provided –why ? because we looked for itemType=3

• for itemType = 10

  3000,0 should be provided –why ? because table has found 3000,10 and this 3000 also has itemType=0
  3000,10 should be provided –why ? because we looked for itemType=10

• for itemType = 11

  4000,11 should be provided –why ? because we looked for itemType=11 ( notice , there isn’t itemType 0 , so only itself).

I started doing :

;with cte as(
             SELECT * FROM @t  
            )
select * from cte where itemType=3

In summary, if the itemType is found, provide itself + its zero type (if exists), and also for his siblings ( sample(#1) )

But I can’t do union here cause CTE is not recognized there… rubbish. it is possible.

How can I solve it ?

SQL ONLINE

Answer 1

To avoid evaluating the itemType = 3 query twice you can self outer join then use CROSS APPLY ... VALUES to UNPIVOT

DECLARE @itemType INT = 3;

WITH T(item1, itemType1, item2, itemType2 )
     AS (SELECT *
         FROM   @t T1
                LEFT JOIN @t T2
                  ON T1.item = T2.item
                     AND T2.itemType = 0
                     AND T1.itemType <> 0
         WHERE  T1.itemType = @itemType) 
SELECT item,
       itemType
FROM   T
       CROSS APPLY ( VALUES (item1, itemType1),
                            (item2, itemType2) ) v(item, itemType) 
WHERE item IS NOT NULL

SQL Fiddle

Execution Plans