Simple logic but not working as it should - sql-server

Question

This is what i want to achieve:
So trigger fires on opportunities table when a record with opp_type = 0 is inserted.
The next part of the code just does the calculation which is to pick up the last used number from your custom table and add 1 to it. Stores new value in a variable.
The next part is to do the insert into the user field.
Finally update the custom table to record the last used number.
I am getting the number to increment by one in the NEXTEXP1 table however the user field called O_Quote is not populating via the GUI.
is the code below doing what it should in terms of the explanation above?
by the steps in my trigger it seems the same but the user field is not populating with last number used:
alter TRIGGER [dbo].[Q2] ON [dbo].[AMGR_opportunity_Tbl] AFTER INSERT
AS
BEGIN
Declare #Opp_Type int
Select #Opp_Type = 0 from inserted
If #Opp_Type = 0
BEGIN
SET NOCOUNT ON;
DECLARE #Client_Id varchar(24)
DECLARE #Contact_Number int
DECLARE #NewNumber varchar(250)
DECLARE #NextQNo float
DECLARE #UDFName varchar(50)
DECLARE #GeneratorPrefix varchar(10)
DECLARE #GeneratorLength float
DECLARE #Opptype int
DECLARE #Type_id int
DECLARE #Oppid varchar (24)
--select top 1 nextqno = nextqno from nextexp1
SELECT #NewNumber = NextQno + 1 from dbo.NextEXP1
----insert into user field
insert into O_Quote(Client_Id, Contact_Number, Type_Id, Code_Id, [O_Quote])
values (#Client_Id,0,15,0,#NextQNo)
-------update table with last number used
UPDATE [dbo].[NextEXP1] SET NextQNo = #NewNumber
End
End
GO

Answer 1

#Leonidas199x is right with all points. I can also say that there are too many things that are unclear with that questions and lot's of the data is missing, however this is what I can suggest (this code handles bulk inserts also):
alter TRIGGER [dbo].[Q2] ON [dbo].[AMGR_opportunity_Tbl] AFTER INSERT
AS
BEGIN
DECLARE #NewNumber varchar(250);
SELECT #NewNumber = MAX(NextQno) FROM dbo.NextEXP1; -- I guess that's what you want
insert into O_Quote(Client_Id, Contact_Number, Type_Id, Code_Id, [O_Quote])
select Client_Id, Contact_Number, Type_Id, Code_Id, #NewNumber + row_num
FROM (
SELECT Client_Id, -- once again do not know where this value is taken from
0 Contact_Number,
15 Type_Id,
0 AS Code_Id,
ROW_NUMBER() OVER(order by client_id) row_num
FROM INSERTED WHERE Opp_Type = 0 --I guess that's the right column name
) a;
SELECT #NewNumber = MAX(O_Quote) FROM O_Quote;
UPDATE [dbo].[NextEXP1] SET NextQNo = #NewNumber;
END

Answer 2

Looking into this, I think your logic is a bit off:
Select #Opp_Type = 0 from inserted
This will always evaluate as 0.
You want to use:
SELECT #Opp_Type = i.Opp_Type
FROM inserted AS i;
Where i.Opp_Type is your column name.
Secondly, you declare a bunch of variables, but never set them:
DECLARE #Client_Id varchar(24)
DECLARE #Contact_Number int
DECLARE #NewNumber varchar(250)
DECLARE #NextQNo float
DECLARE #UDFName varchar(50)
DECLARE #GeneratorPrefix varchar(10)
DECLARE #GeneratorLength float
DECLARE #Opptype int
DECLARE #Type_id int
DECLARE #Oppid varchar (24)
And then go on to insert them. You need to set these, if you want to use them later. Should this be:
insert into O_Quote(Client_Id, Contact_Number, Type_Id, Code_Id, [O_Quote])
values (#Client_Id,0,15,0,#NewNumber)
Or do you need to set #NextQNo to be:
SELECT #NextQNo = NextQno from dbo.NextEXP1;
SELECT #NewNumber = #NextQNo + 1;
And lastly, the way this is written will cause you issues if you insert more than one record at a time. You would need to think about a loop, to get that MaxID, which isn't ideal. Can you look at using IDENTITY columns instead?