Re: interesting sequence

That's why you need to do this inside a function. Basically just make
an insert function for the table and have it calculate the count and
do the insert in one transaction.

On Tue, Jul 5, 2011 at 5:41 PM, Samuel Gendler
<sgendler(at)ideasculptor(dot)com> wrote:
>
>
> On Tue, Jul 5, 2011 at 2:42 PM, John Fabiani <johnf(at)jfcomputer(dot)com> wrote:
>>
>> On Tuesday, July 05, 2011 01:11:11 pm Kevin Crain wrote:
>> > You don't need a loop there.  Assuming your order id field is of type
>> > varchar you can just build the first part of your string and then do a
>> > count to get the last part using a LIKE comparison:
>> >
>> > select count(id_order) + 1  from sometable WHERE id_order LIKE
>> > 'O-20110704
>> > -%';
>> >
>> > If you do this inside a function it will be like running it in a
>> > transaction so you shouldn't have to worry about it being a multi-user
>> > system.
>> >
>> >
>> >
>>
>> I like this - looks better than what I'm currently doing.  Thanks
>> Johnf
>>
>
> It is simpler, but it will result in id collision if two inserts runs at the
> same time, particularly if the count query takes a while to run, so be
> prepared to handle that.  Make sure you have an index which can satisfy that
> count query quickly.  If you are not using the C locale for your database,
> that means you must create an index on that column that uses
> text_pattern_ops or varchar_pattern_ops (depending on if it is text or
> varchar column) so that postgresql can use the index for that comparison,
> otherwise LIKE clauses will force a sequential scan of the whole table every
> time.  C locale does byte by byte text comparison, so the special index
> isn't required.
> http://www.postgresql.org/docs/9.0/interactive/indexes-opclass.html
>
>