How to get one common value from Database using UNION

2 records in above image are from Db, in above table Constraint are (SID and LINE_ITEM_ID), SID and LINE_ITEM_ID both column are used to find a unique record.

My issues : I am looking for a query it should fetch the recored from DB depending on conditions if i search for PART_NUMBER = 'PAU43-IMB-P6开发者_Python百科' 1. it should fetch one record from DB if search for PART_NUMBER = 'PAU43-IMB-P6', no mater to which SID that item belong to if there is only one recored either under SID =1 or SID = 2. 2. it should fetch one record which is under SID = 2 only, from DB on search for PART_NUMBER = 'PAU43-IMB-P6', if there are 2 items one in SID=1 and other in SID=2.

i am looking for a query which will search for a given part_number depending on Both SID 1 and 2, and it should return value under SID =2 and it can return value under SID=1 only if the there are no records under SID=2 (query has to withstand a load of Million record search).

Thank you

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Select * 
  from Table
 where SID||LINE_ITEM_ID = (
                            select Max(SID)||Max(LINE_ITEM_ID) 
                              from table 
                             where PART_NUMBER = 'PAU43-IMB-P6'
                           );

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If I understand correctly, for each considered LINE_ITEM_ID you want to return only the one with the largest value for SID. This is a common requirement and, as with most things in SQL, can be written in many different ways; the best performing will depend on many factors, not least of which is the SQL product you are using.

Here's one possible approach:

SELECT DISTINCT * -- use a column list
  FROM YourTable AS T1
       INNER JOIN (
                   SELECT T2.LINE_ITEM_ID, 
                          MAX(T2.SID) AS max_SID 
                     FROM YourTable AS T2
                    GROUP
                       BY T2.LINE_ITEM_ID
                  ) AS DT1 (LINE_ITEM_ID, max_SID)
          ON T1.LINE_ITEM_ID = DT1.LINE_ITEM_ID 
             AND T1.SID = DT1.max_SID;

That said, I don't recall seeing one that relies on the UNION relational operator. You could easily rewrite the above using the INTERSECT relational operator but it would be more verbose.

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Well in my case it worked something like this:

select LINE_ITEM_ID,SID,price_1,part_number from (
(select LINE_ITEM_ID,SID,price_1,part_number from Table where SID = 2)
 UNION 
(select LINE_ITEM_ID,SID,price_1,part_number from Table  SID = 1 and line_item_id NOT IN (select LINE_ITEM_ID,SID,price_1,part_number from Table  SID = 2)))

This query solved my issue..........