Re: Function with limit and offset - PostgreSQL 9.3

[marcinha rocha <marciaestefanidarocha@xxxxxxxxxxx>]

On 6/8/2017 5:53 PM, marcinha rocha wrote:

> Hi guys! I have the following queries, which will basically select
> data, insert it onto a new table and update a column on the original
> table.

I'm sure your example is a gross simplification of what you're really

doing, but if that's really all you're doing, why not do it all at once,

instead of row at a time?

BEGIN;

     insert into tableb (id) select id from tablea;

     update tablea set migrated=true;

COMMIT;

thats far more efficient that the row-at-a-time iterative solution you

showed.

You're right, that is just an example.

I'm basically using a CTE to select the data and then, inserting some rows onto a new table.

I just don't know how to tell my function to perform 2000 records at once, and then when calling it again it will "know" where to start from

Maybe, I already have everything I need?

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

On my original select, the row will have migrated = false. Maybe All I need to put is a limit 2000 and the query will do the rest?

Example:

CREATE or REPLACE FUNCTION migrate_data()
RETURNS integer;

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';