max value in insert into - sql

Question

I need to get the maximum number in a column because in a insert operation I have to insert max number in that column +1 for each insert, I did this:
insert into table1(id ,.., field,...)
select newid(), ..., (SELECT CONVERT(VARCHAR(8), FORMAT((MAX(number)+1),'00000000'))
FROM table1)
It works just for the first inserted row, than I get this number for other rows too!

Answer 1

This is too long for a comment.
Why aren't you using an identity column? You can define the number as:
number int identity(1, 1)
If you want the value as a string padded to eight characters, then use a computed column:
number_string as (format(number, '00000000'))
EDIT:
There are strong reasons why you want an identity column and not to calculate the values yourself. You can do what you want using row_number(), where the logic looks like this:
insert into table1(id ,.., field,...)
select newid(), ...,
convert(varchar(8),
(coalesce(t1.max_number, 0) +
row_number() over (order by (select null))
)
)
from table2 t2 cross join
(select max(t1.number) as max_number from table1 t1) t1;
N
Note: I am assuming that the inserts are coming from a different table, but table2 can really be table1.
Very importantly: This is not thread safe. Two different threads can run the same code and result in the same values. The solution to this is locking the entire table. However, that can have very significant performance impacts.

Answer 2

There's a lot to comment on here, and like Gordon, I can't fit it into one.
Firstly, I notice you have a column id and you're inserted the value NEWID() into it. I therefore hope that id isn't your CLUSTERED INDEX, as if it is NEWID() is not doing it any favours. If you are using a uniqueindentifier for your CLUSTERED INDEX, use NEWSEQUENTIALID() instead, and don't provuide the value in the INSERT:
ALTER TABLE dbo.Table1 ADD CONSTRAINT DF_Table1_id DEFAULT NEWSEQUENTIALID() FOR id;
As for your INSERT, as I said in my comment: "Use an IDENTITY column. If you must then have sequential values, use a VIEW and ROW_NUMBER. Let SQL Server gracefully handle the incrementing value. Trying to increment the number yourself is going to only cause you problems, such as race conditions, and your data will be in a far worse position.". Unfortunately you can't change an existing column to an IDENTITY, so this is a little harder. Likely you'll want to do something like:
ALTER TABLE dbo.Table1 ADD number_new int IDENTITY(1,1);
GO
SET IDENTITY_INSERT dbo.Table1 ON;
--UPdate the new column with the existing values
UPDATE dbo.Table1
SET number_new = number;
SET IDENTITY_INSERT dbo.Table1 OFF;
GO
--Drop the old column and rename
ALTER TABLE dbo.Table1 DROP COLUMN number;
EXEC sp_rename N'dbo.Table1.number_new', N'number', N'COLUMN'
As Gordon said, if you simply then need a formatted value (with leading 0's) and no worry about gaps, use a computed column:
ALTER TABLE dbo.Table1 ADD Number_f AS RIGHT(CONCAT('00000000',number),8) PERSISTED;
If, however, you want them to be in sequential order, and update accordingly when a row is deleted, or a INSERT fails, etc, then you can use a view, with the following expression:
RIGHT(CONCAT('00000000',ROW_NUMBER() OVER (ORDER BY number ASC),8)

Answer 3

You can use a ROW_NUMBER() function to increment the IDs. Just replace the +1 with ROW_NUMBER() OVER(). Something like this:
insert into table1(id ,.., field,...)
select (SELECT MAX(number) FROM table1) + ROW_NUMBER() OVER(ORDER BY <field1>), ...
from table1
SQL Fiddle