Question

Hello I want to Update 1 table based on value present in other table. I could use Join to write the update statement and infact I have written it and it works using Join. But out of curiosity I want to use CTE. I wrote the following query but it doesn’t seem to work. Can anybody tell me what the issue is? Does CTE require Select statement at the end compulsorily? Why can I not write Update statement?

WITH cte(uid, col1)
As
(
    Select uid, col1
        From [User]
)
Update t2
    Set col1 = cte.col1
        Where uid = cte.uid

Answer 1

You still need to join back to your CTE, like so

WITH cte([uid], col1)
As
(
    Select [uid], col1
        From [User]
)
Update t2
    Set col1 = cte.col1
    FROM t2 inner join cte cte 
    on t2.[uid] = cte.[uid]

Edit I guess you could avoid the ‘JOIN’ keyword by using old-style SQL WHERE joins, but this isn’t really good practice.

...        
FROM t2, cte cte 
WHERE t2.[uid] = cte.[uid]

Also note that you can also update through the CTE, like views, as long as you only update one table.

WITH cte(userCol1, t2Col1)
As
(
    Select [u].col1 as userCol1, t2.col1 as t2Col1
        From [User] u
        inner join t2
         ON u.[uid] = t2.[uid]
)
Update cte
    Set t2Col1 = userCol1