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POCan a CTE be used to update in passes?
 

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  1. POCan a CTE be used to update in passes?
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    <p>I inherited a table with the following structure:</p> <pre><code>rowID rn userID Data1 Data2 Data3 ----- -- ------ ----- ---- ---- 1 1 1 A null 123 2 2 1 B 111 null 3 1 2 C 222 333 4 2 2 D null null 5 3 2 E 111 null 6 1 3 F 333 222 </code></pre> <p>The first recs (<code>rn=1</code>) need to be inserted, while the rest (<code>rn &lt;&gt;1</code>) need to update the insertions (sequentially). I can insert easily, using <code>where rn = 1</code> and checking for absence of the userID.</p> <p>My problem is that I need to now update all recs sequentially using <code>rn &lt;&gt;1</code> so that the user table reflects the latest state. That is, the user table after UPDATEs should look like this:</p> <pre><code>rowID userID Data1 Data2 Data3 ----- ------ ----- ----- ----- 1 1 B 111 123 2 2 E 111 333 3 3 F 333 222 </code></pre> <p>My thought was to write a CTE, where each "pass" would grab all the recs where rn=2, then rn=3, then rn=4.... until I have no more rn to process. This way, I can update in sets.</p> <p>Is this possible (or should I use do-while)? if so, do I need a recursive one or a "regular" CTE? </p> <p>Here is what I tried:</p> <pre><code>;with my_cte (rowID, rn, userID, Data1, Data2, Data3, val) As ( SELECT rowID, rn, userID, Data1, Data2, Data3, val from @MyTempTable x where rn =1 UNION ALL SELECT rowID, rn, userID, Data1, Data2, Data3, b.val +1 from @MyTempTable y INNER JOIN my_cte b ON y.userID = b.userID WHERE y.rn = b.val +1 ) UPDATE userTable SET [Data1] = COALESCE(c.Data1, [Data1]) ,[Data2]= COALESCE(c.Data2, [Data2]) ,[Data3]= COALESCE(c.Data3, [Data3]) From @MyTempTable c JOIN ( SELECT user_id FROM my_cte WHERE rn&lt;&gt;1 ) b ON b.user_id = c.user_id WHERE EXISTS ( Select userID from userTable q Where q.userId = b.userId ) </code></pre> <p>I could not get this to work, and it looks like only the first row is updating. Any thoughts? I'm a noob with CTEs. More than anything I'd like to know what exactly the CTE is doing... is it even possible for the update to run in "passes"?</p>
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    1. USuser991945
    1. USuser991945
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      1. POCan a CTE be used to update in passes?
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      1. VTUpMod
    1. COShouldn't `Data1` for `userID` 1 be **B** and what is your current maximum `rn`?
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      1. USLieven Keersmaekers
    2. CO@Lieven, you are right. I edited the original post. I don't know what rn could be. It's currently up to 19, and I could go higher I'm sure.
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      1. USuser991945
 

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