Carlos Mennens wrote on 11.05.2012 21:03:
I have a problem in SQL I don't know how to solve and while I'm sure
there are 100+ ways to do this in ANSI SQL, I'm trying to find the
most cleanest / efficient way. I have a table called 'users' and the
field 'users_id' is listed as the PRIMARY KEY. I know I can use the
COUNT function, then I know exactly how many records are listed but I
don't know what the maximum or highest numeric value is so that I can
use the next available # for a newly inserted record. Sadly the
architect of this table didn't feel the need to create a sequence and
I don't know how to find the highest value.
You can get the highest value using:
select max(users_id)
from users;
But that method is neither safe in a multi-user environment nor fast.
But you can always assign a sequence to that column even if it wasn't done
right at the start:
Create a new sequence owned by that column:
create sequence seq_users_id
owned by users.users_id;
Now set the value of the sequence to the current max. id:
SELECT setval('seq_users_id', max(users_id)) FROM users;
And finally make the users_id column use the sequence for the default value:
alter table users alter column users_id set default nextval('seq_users_id');
Thomas
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