Обсуждение: getting a sequence to update properly
I'm trying to add a sequence function to an already existing field. All the 4000 records for this table currently have a value already in this field, but I'd like new ones to just get the next value by default as opposed to users being forced to type something. What I'd like to do is to reload this table and get the field to be updated by the sequence on the reload. I thought that by dumping the table with pg_dump and reloading with the generated datafile, this would happen, but the sequence's last_value field didn't change. Apparently, the values contained in the dump file won't update the sequence. Short of thoroughly massaging the datafile generated by the dump and turning all those record lines into SQL INSERT statements, is there any way to effectively update a field for an existing record so that the field gets the value from the sequence? I would normally just set minimum value to something greater than what already in the table, but the manually keyed values are all over the place, and I guess I'd really like to remove the gaps in the current values.
--
John
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> I would normally just set minimum value to something greater than what
> already in the table,
That's the way to go.
> but the manually keyed values are all over the place, and I guess I'd
> really like to remove the gaps in the current values.
You'll have to do that yourself, perhaps with a plpgsql function or
an perl script. Here's a quick little function that should do the
job: give it a tablename and a column. The column must contain
unique, positive ids. After running, just slap a default nextval
on the column with a sequence starting at one above the number returned
and you're done.
CREATE OR REPLACE FUNCTION removeholes(text,text) RETURNS INT LANGUAGE plpgsql AS
$$
DECLARE
T ALIAS FOR $1;
C ALIAS FOR $2;
myst TEXT;
mycount INT := 0;
myrec RECORD;
BEGIN
myst := 'UPDATE '||T||' SET '||C||' = -'||C;
EXECUTE myst;
myst := 'SELECT '||C||' FROM '||T||' ORDER BY '||C||' DESC ';
FOR myrec IN EXECUTE myst LOOP
mycount := mycount + 1;
myst := 'UPDATE '||T||' SET '||C||' = '||mycount||' WHERE '||C||' = '||myrec.id;
EXECUTE myst;
END LOOP;
RETURN mycount;
END;
$$;
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Greg Sabino Mullane greg@turnstep.com
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