Multiple statements with one cte? - sql

Question

What is the correct syntax for the following? (I need these in one query)
--- 1. task
update A set .... where ....
insert into A (...) values (...);
--- 2 .task
With cte as (select A.column...)
update A set ... if condition1(includes cte table)
update A set ... if condition2(includes cte table)
update A set ... if condition3(includes cte table)
In words:
I update table A or insert into it
After that I refer to this updated TableA in a cte table, which contains a ROW_NUMBER function,
And then I want to update TableA again depended on that rownumber from CTE in a specific row, for example: if rownumber value in the CTE is 1, do this, if it is max(rownumber) for that specific row then do that....
I read that cte-s only persist for a single statement. I tried to copy the cte for every update statement, separated with semicolons, but that didn't work. I read about MERGE but I'm not sure if this is the right way for that. Is it the OUTPUT clause, if yes, how to use it? Or something else? Can you help me please?

Answer 1

You don't need multiple update statement. You can do with one.
; WITH CTE as ( select . . . )
UPDATE A
SET col1 = case when .... then new_1 else col1 end,
col2 = case when .... then new_2 else col2 end
FROM CTE as A

Answer 2

For anyone who tries to avoid copy-paste and wants to reuse some complex query from CTE to perform multiple statements, probably temporary table would work for you:
select A.column as AnyColumn, ... into #NameYouWant from A, ...
update A set column1 = (select AnyColumn from #NameYouWant where ...)
update B set column2 = (select AnyColumn from #NameYouWant where ...)
update C set column3 = (select AnyColumn from #NameYouWant where ...)
Please note that number sign (#) in table name is important, it will indicate that table is temporary, so it would persist only within your current session.

Answer 3

Correct, a CTE only persists in the statement it exists in. Therefore a statement like the following will fail:
WITH CTE AS(
SELECT *,ROW_NUMBER() OVER (PARTITION BY Date ORDER BY ID) AS RN
FROM YourTable)
SELECT *
FROM CTE
WHERE RN = 1;
SELECT *
FROM CTE
WHERE RN = 2;
That's because the CTE no longer exists during the second statement.
For an UPDATE (or any statement ) you'll therefore need to redeclare your CTE each time. Thus, using the example above, you would have to do:
WITH CTE AS(
SELECT *,ROW_NUMBER() OVER (PARTITION BY Date ORDER BY ID) AS RN
FROM YourTable)
SELECT *
FROM CTE
WHERE RN = 1;
WITH CTE AS(
SELECT *,ROW_NUMBER() OVER (PARTITION BY Date ORDER BY ID) AS RN
FROM YourTable)
SELECT *
FROM CTE
WHERE RN = 2;
If the expressions within the CTE are quite complex, and you use them often, you might instead consider using a VIEW.