There is no connection between the table you're deleting from and the EXISTS clause.  If the EXISTS is ever true for the tables it references, even for just one row,...

That's one of the reasons SQL allows NULL "values" in columns (NULL is technically not a value, it's the absence of a value; for day-to-day purposes, you can think of...

It's easy enough to get a list of the missing values.  But getting a concatenated list is somewhat more difficult.

;WITH cte_packages AS (
   ...

The "WITH" from a CTE can cause errors if not preceded by a ; if an actual statement preceded the WITH.  Therefore it's safer to prepend a ; so that...

In the WHERE clause, don't.

WHERE (@chan_id IS NULL OR tablea.chan_id = CAST(@chan_id AS...

As in your original method, you don't need to calc everyone's age, just check the correct date range.  Like this:

WHERE Birthdate >= DATEADD(DAY, 1, DATEADD(YEAR,...

No.  Actually, in RC level, the...

You can, but you shouldn't.  If you're creating only one index on a temp table, make it a clustered index not a non-clus index; the key columns don't have to...

Don't sort the query, sort the result table instead, which is more useful anyway.  Even if sort the query, you will still have to sort again when reading from the...