UPDATE with LIMIT / OFFSET in PL/pgSQL function In my Postgres 9.2 database I've got the following SELECT, which will be used by a PL/pgSQL function:

SELECT
      id
FROM
      tablea
WHERE
      migrated = false;


I want to get 2000 records each time and perform something like the following:

CREATE or REPLACE FUNCTION migrate_data()
RETURNS integer AS
$$
declare
        row record;

BEGIN

FOR row IN EXECUTE '
        SELECT
              id
        FROM
              tablea
        WHERE
              migrated = false
'
LOOP

INSERT INTO tableb (id)
VALUES (row.id);

UPDATE tablea a SET migrated = yes WHERE a.id = row.id;

END LOOP;

RETURN num_rows; -- I want it to return the number of processed rows

END

$$ language 'plpgsql';


How can I tell the function to process 2000 records with every call? And it must start from where it left when on the next call.

Example:

select migrate_data(); -- id 0 to id 2000

select migrate_data(); -- id 2001 to id 4000

select migrate_data(); -- id 4001 to id 6000

select migrate_data(); -- id 6001 to id 8000


Etc.
It will be much simpler (and faster) to use cursors for that:

begin;
declare foo cursor for
    SELECT
          id
    FROM
          tablea
    WHERE
          mig = true;
fetch forward 2000 from foo;
fetch forward 2000 from foo;
-- etc
rollback;


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About fetch