How to do these three things in a SQL Server transaction - 1. create table, 2.create trigger on table, 3. select from another table - sql

Question

I am trying to accomplish the following 3 simple tasks as a transaction (i.e. I need to lock old_table and new_table until the process completes).
Create a new table (new_table)
Add a trigger to old_table, which queues updates to new_table.
Select all the data from old_table and return it.
Note that I want these handled in a single transaction. I cannot allow inserts into old_table (and therefore triggered inserts into new_table) in between the trigger creation and the select on old_table.
My current closest attempt is this, but truthfully I feel that I am very far off from accomplishing my goal with this code. I have added the code just for reference of what I am trying, but I am mostly interested in non-specific answers that layout how to accomplish the above three comands in a transaction.
DROP PROCEDURE IF EXISTS dbo.BuildAll;
CREATE PROCEDURE dbo.BuildAll
AS
BEGIN
BEGIN TRANSACTION
DECLARE #TriggerCode VARCHAR(MAX)
CREATE TABLE dbo.new_table
(
status nvarchar(5),
type char(1),
col1 nvarchar(50),
col2 smallint
)
SELECT #TriggerCode = 'CREATE TRIGGER myTrigger
ON dbo.old_table FOR INSERT
AS
DECLARE #col1_new nvarchar(50)
DECLARE #col2_new smallint
SELECT #col1_new = col1 FROM inserted
SELECT #col2_new = col2 FROM inserted
IF #col1_new IS NOT NULL
BEGIN
INSERT INTO new_table (status, type, col1, col2)
SELECt "Q", "A", #col1, #col2 FROM inserted
END'
EXEC(#TriggerCode)
SELECT * FROM old_table
COMMIT
END

Answer 1

Going to suggest this an a possible solution you can try. This doesn't address the correctness of your actual trigger, you have two separate questions here really.
You don't need to encapsulate this entire process in a transaction.
Create your new table.
Create your trigger on old table, but disabled.
set transaction isolation level serializable
begin tran
go
create trigger <Name> on <Table> etc
go
disable trigger <Name> on <Table>
go
commit
Now in a transaction you can lock the old table against other activity while you work
begin tran
update oldtable with(tablockx) set column=column where id=0 /* block other processes from updating table, id=0 row doesn't exist */
query your data and process as required
enable trigger <Name> on <Table>
commit

Answer 2

This trigger code of yours is kinda odd .... you have a trigger on all three operations - yet it appears as if you're never using the values you fetch from the deleted pseudo table, and if the value from the inserted table is NULL, you're not doing anything inside your trigger - so you can really spare yourself the DELETE case - that'll never do anything....
Also, as mentioned in my comment - you Inserted pseudo table can easily contain multiple rows - but you're selecting from it as if you only ever expect it to contain a single row.
You should really rewrite your trigger code to handle the case of multiple rows in Inserted and make the whole thing properly set-based - something like this:
CREATE TRIGGER myTrigger
ON dbo.old_table
FOR INSERT, UPDATE
AS
INSERT INTO new_table (status, type, col1, col2)
SELECT 'Q', 'A', i.col1, i.col2
FROM Inserted i
Whether you need this on the UPDATE case at all - I cannot tell, you need to decide this. But basically: just select from the Inserted table, take the Col1 and Col2 values, and add the constant values 'Q' and 'A' to your insert to handle multiple rows properly. That should do it.