Re: Support retrieving value from any sequence

On Tue, Jul 14, 2015 at 10:52 AM, Thom Brown <thom(at)linux(dot)com> wrote:
> When using currval() to find the current value of all sequences, it chokes
> on those that aren't initialised. This is expected and documented as
> behaving in this manner. However, I think it would be useful to also
> support retrieving the current value of a sequence, regardless of whether
> it's been used. As this wouldn't be to get a sequence value for the current
> session, but all sessions, this would ideally get the real current value.
>
> The use-case I have in mind is for finding out how close to the 32-bit
> integer limit sequences have reached. At the moment, this isn't possible
> without creating a custom function to go fetch the last_value from the
> specified sequence.
>
> So would it be desirable to have a function which accepts a sequence
> regclass as a parameter, and returns the last_value from the sequence?
>
> Effectively, the same result as what this provides:
>
> CREATE FUNCTION lastval(tablename regclass) RETURNS bigint AS $$
> DECLARE
> last_value bigint;
> BEGIN
> EXECUTE format('SELECT last_value FROM %I ', tablename) INTO last_value
> USING tablename;
> RETURN last_value;
> END
> $$ LANGUAGE plpgsql;

Since it's trivial to define this function if you need it, I'm not
sure there's a reason to include it in core.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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