How to implement priorities in SQL (postgres)

Question

I\'m writing some software that requires storing items in a database, the items need to have a \'priority\' so we end up with

    ID  |  Name        |  Priority
         


        

Answer 1

Two updates in a single transaction should work fine on a such small table.

create temp table priorities (
  id integer primary key,
  name varchar(15) not null,
  priority integer not null check (priority > 0 and priority < 100)
);

insert into priorities values 
(1,'Pear',4),
(2,'Apple',2),
(3,'Orange',1),
(4,'Banana',3);

-- Make Pear priority 1.
begin;
update priorities 
set priority = priority + 1
-- The value below is the priority you're aiming for. You want
-- Pear to be #1, so you use ">= 1".
where priority >= 1;

update priorities
set priority = 1 where name = 'Pear';
commit;

For convenience, you can wrap this in a stored procedure.