If the reccord you are inserting do not depend on data in the record you
want to delete, why not simply use a trigger?
Before insert delete the record with the same key!
Michael Paesold wrote:
> Tsirkin Evgeny wrote:
>
>
>
>>one moer question ,how did you tested it?
>>
>>
>>>I have tested this here. I don't really know if this is just the case
>
> with
>
>>>Best Regards,
>>>Michael Paesold
>
>
> First I created the your schedule table. Then I opened two psql sessions...
>
> Session A Session B
>
> BEGIN;
> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
> DELETE FROM schedule WHERE studentid = 1;
> INSERT INTO schedule VALUES (1, 1, 0, 0);
>
> BEGIN;
> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
> DELETE FROM schedule WHERE studentid = 1;
> -- if there existed records for this delete,
> -- session B will now wait for session A to
> -- commit/rollback and error out on commit;
> -- otherwise no error
>
>
> COMMIT;
> INSERT INTO schedule VALUES (1, 1, 0, 0);
> COMMIT;
>
>
> You can also try and rollback the first transaction etc.
>
> Again, what really helps is:
> ALTER TABLE schedule ADD CONSTRAINT uniq_schedule UNIQUE (studentid,
> groupid);
>
> Best Regards,
> Michael Paesold
>
>
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