A sequence is very easily implemented as a virtual table that keeps the current
values in a separate table my_sequences (name text primary key, initial
integer, current integer, increment integer).
CREATE VIRTUAL TABLE seq_1 USING sequence ([<initial>[,<increment>]]); --
defaults 1, 1
The xCreate/xConnect function just needs to store its name and set a DDL like
CREATE TABLE X (current_value integer, next_value integer);
The xColumn function just needs to run one of two statements:
For field next_value run the following statement and fall through to
current_value:
UPDATE my_sequences SET current = current + increment WHERE
name='<sequence_name>';
For field current_value:
SELECT current FROM my_sequences WHERE name='<sequence name>';
You could also implement a virtual field rewind
UPDATE my_sequences SET current = initial WHERE name='sequence_name';
Or whatever else tickles your fancy. Just think table <=> class, virtual field
<=> method
-----Ursprüngliche Nachricht-----
Von: sqlite-users [mailto:[email protected]] Im
Auftrag von Sylvain Pointeau
Gesendet: Mittwoch, 02. August 2017 21:07
An: SQLite mailing list <[email protected]>
Betreff: Re: [sqlite] sequencer
ok thank you for the confirmation, I will try implementing it in a dll using UD
functions and put it on github.
Le mer. 2 août 2017 à 20:56, Richard Hipp <[email protected]> a écrit :
> On 8/2/17, Sylvain Pointeau <[email protected]> wrote:
> >
> > is it really possible to make an update into that nextval function?
> > I
> don't
> > think so since only one statement can be run at the same time if
> > sqlite
> is
> > in serialized mode.
>
> "serialized" means that multiple threads cannot be making updates at
> the same time. In this case, the update would be happening in the
> same thread.
>
> --
> D. Richard Hipp
> [email protected]
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> sqlite-users mailing list
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>
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