Could you post a CREATE TABLE script and an INSERT script to populate it?
I think you can use Jeff Moden's DelimitedSplit8K function to break the individual attributes...

I think this is close... back up your table or wrap this in a transaction and roll it back when testing.. The INTERSECT returns the DuplicatingValue where there is at...

Could you post the CREATE TABLE script for the expected result?
It seems that you could do this using a combination of the windowing function LAG() and STUFF() to concatenate...

DelimitedSplit8K is your friend.

Happy reading. Happy learning.

Something like this:
CREATE TABLE Insurance (
    RecordNo INT IDENTITY,
    PolicyNo INT NOT NULL);
GO

INSERT INTO Insurance (PolicyNo)
VALUES (34564),(67548),(34564),(98271),(90198),(98271);

CTE to identify and delete...

Oh, FFS, Got Google?
https://www.databasejournal.com/features/mssql/managing-sql-server-services-with-powershell.html
should give you a pretty good idea.

Then use OUTER APPLY instead of CROSS APPLY.

why what works? The ROW_NUMBER() OVER (PARTITION...) part?
PARTITION OVER is super simple - it's analogous to grouping in a totals/aggregate query, but you still get the individual records, which...

I find it hard to believe you've been coding this long (and asking questions) and can't write a simple correlated subquery.

Say I want to show all the details...

You could use
WHERE EXISTS  and correlated subqueries. It will slow things down, but right answers are better than fast answers.

Do you inherit these stored procedures or...

Thanks Sue. I'll have a look.
I may not have been thinking... probably the really simple answer is "Mark the optional parameters as optional!"  Yeah, "here's my sign!" =)

Could you explain what this does? (Is this Oracle?)
SELECT
@Od = :a2,
@Do = :a3,
@TipSobe = :a1,
@KodaCenika = :a4;

It's probably not a syntax issue. It's a permissions issue. If it were a syntax issue, the code would stop and you'd get an error message that the T-SQL "statement...