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POCan this row-by-row T-SQL script be converted to a set-based script?
 

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  1. POCan this row-by-row T-SQL script be converted to a set-based script?
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    <p>I have written this T-SQL script to roll up duplicate rows in a database that are created by a reconstruction process. To do this, it performs the following:</p> <ul> <li>Gets and stores the minimum target table primary key (ColTargetPK) per set of duplicate entries in a table variable (@minColTargetPKTable); determining duplicates by matching on three columns - ColIntA, ColIntB and ColDateTimeA.</li> <li>Sets the Target Column to be rolled up (TargetColVarchar) to equal a concatenation of the target column of the corresponding duplicate entries.</li> <li>Flags the duplicate entries as inactive (ColTargetStatus = 0)</li> <li>Reports success (or failure)</li> </ul> <p>Due to the size of the dataset involved, this script takes an inappopriate length of time to run. </p> <p>Can anyone see how this can be converted to be set-based, if so, could you please provide an example?</p> <p>I apologise in advance if my description is a bit confusing...</p> <pre><code>declare @MinColTargetPKTable table (ColIntA int, ColIntB int, ColDateTimeA nvarchar(25), minColTargetPK int ) insert @minColTargetPKtable select ColIntA, ColIntB, convert(nvarchar(25),ColDateTimeA,120) as ColDateTimeA, min(ColTargetPK) as MinColTargetPK from TargetColTable group by ColIntA, ColIntB, convert(nvarchar(25),ColDateTimeA,120) declare @TargetColVarchar varchar(max) declare @updatedColTargetPKs table (updatedColTargetPKs int) declare @minColTargetPK int declare cur cursor for select minColTargetPK from @minColTargetPKtable open cur fetch next from cur into @minColTargetPK while @@FETCH_STATUS = 0 begin begin try set @TargetColVarchar = convert(nvarchar(max),( select replace(convert(nvarchar(max), isnull(TargetColVarchar,'')) + convert (nvarchar(max),' \par \par \par'), '\par } ', '\par') as TargetColVarchar from TargetColTable v1 where ColIntA = (select ColIntA from TargetColTable where ColTargetPK = @minColTargetPK) and ColIntB = (select ColIntB from TargetColTable where ColTargetPK = @minColTargetPK) and convert(nvarchar(25),ColDateTimeA,120) = (select convert(nvarchar(25),ColDateTimeA,120) from TargetColTable where ColTargetPK = @minColTargetPK) order by ColTargetPK for xml path(''), type )) set @TargetColVarchar = REPLACE(REPLACE (REPLACE (@TargetColVarchar,'&lt;TargetColVarchar&gt;',''),'&lt;/TargetColVarchar&gt;',''), '&amp;#x0D;','') update TargetColTable set TargetColVarchar = @TargetColVarchar where ColTargetPK = @minColTargetPK update TargetColTable set ColTargetStatus = 0 from TargetColTable v1 where ColIntA = (select ColIntA from TargetColTable where ColTargetPK = @minColTargetPK) and ColIntB = (select ColIntB from TargetColTable where ColTargetPK = @minColTargetPK) and convert(nvarchar(25),ColDateTimeA,120) = (select convert(nvarchar(25),ColDateTimeA,120) from TargetColTable where ColTargetPK = @minColTargetPK) and ColTargetPK != @minColTargetPK Print 'Merge complete for ColTargetPK '+ convert(varchar(50), @minColTargetPK) end try begin catch Print 'Merge failed for ColTargetPK '+ convert (varchar(20),@minColTargetPK) end catch fetch next from cur into @minColTargetPK end close cur deallocate cur </code></pre> <p>EDIT: Ok, below is the script moved to a set-based operation using Preet's suggestion. To give some additional background, TargetTable is approximately 1.1 million rows. Strangely enough, the set-based script below is not significantly faster than the cursor-based script below on the same subset of data (approx. 20000 rows) over 2 trials. Any thoughts on why this wouldn't be faster?</p> <pre><code>declare @minColTargetPKTable table ( ColIntA int, ColIntB int, ColDateTimeA nvarchar(25), ColTargetPK int, concTargetCol varchar(max) ) insert @minColTargetPKtable (minColIntA,ColIntB,minColDateTimeA,minColTargetPK) select ColIntA, ColIntB, convert(nvarchar(25),ColDateTimeA,120) as ColDateTimeA, min(ColTargetPK) as minColTargetPK from TargetTable group by ColIntA, ColIntB, convert(nvarchar(25),ColDateTimeA,120) update @minColTargetPKTable set concTargetCol = (REPLACE(REPLACE(REPLACE(replace(convert(nvarchar(max), ( select convert(nvarchar(max), isnull(TargetColVarchar,'')) + convert (nvarchar(max),' \par \par \par ') as TargetColVarchar from TargetTable v1 where ColIntA = (select ColIntA from TargetTable where ColTargetPK = minColTargetPK) and ColIntB = (select ColIntB from TargetTable where ColTargetPK = minColTargetPK) and convert(nvarchar(25),ColDateTimeA,120) = (select convert(nvarchar(25),ColDateTimeA,120) from TargetTable where ColTargetPK = minColTargetPK) order by ColTargetPK for xml path(''), type )) , '\par } ', '\par '),'&lt;TargetColVarchar&gt;',''),'&lt;/TargetColVarchar&gt;',''), '&amp;#x0D;','')) update TargetTable set TargetColVarchar = mv.concTargetCol from @minColTargetPKTable mv where mv.minColTargetPK = TargetTable.ColTargetPK update TargetTable set TargetColStatus = 0 from TargetTable v inner join @minColTargetPKTable mv on mv.minColIntA = v.ColIntA and mv.minColDateTimeA = convert(nvarchar(25),v.ColDateTimeA,120) and mv.ColIntB = v.ColIntB where ColTargetPK not in (select minColTargetPK from @minColTargetPKTable) </code></pre>
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