CODEWITHSUNDEEP
postgresqlplpgsql
mi ho
mi ho

Reputation: 31

postgresql: USING CURSOR for extracting data from one database and inserting them to another

here is another algorithm using cursor but i'm having a hard time fixing its error ...

CREATE OR REPLACE FUNCTION extractstudent()
RETURNS VOID AS 
$BODY$
DECLARE
    studcur SCROLL cursor FOR SELECT fname, lname, mname, address FROM student;
BEGIN    
    open studcur; 

    Loop
    --fetching 1 row at a time
    FETCH First FROM studcur;
    --every row fetched is being inserted to another database on the local site
    --myconT is the name of the connection to the other database in the local site
    execute 'SELECT * from dblink_exec(''myconT'', ''insert into temp_student values(studcur)'')';
    --move to the next row and execute again
    move next from studcur;
    --exit when the row content is already empty
    exit when studcur is null;
    end loop;

    close studcur;    

END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION extractstudent() OWNER TO postgres;

Upvotes: 3

Views: 15318

Answers (2)

araqnid
araqnid

Reputation: 133792

You rarely need to explicitly use cursors in postgresql or pl/pgsql. What you've written looks suspiciously like a SQL Server cursor loop construct, and you don't need to do that. Also, you can use "PERFORM" instead of "EXECUTE" to run a query and discard the results: this will avoid re-parsing the query each time (although it can't avoid dblink parsing the query each time).

You can do something more like this:

DECLARE
  rec student%rowtype;
BEGIN
  FOR rec IN SELECT * FROM student
  LOOP
    PERFORM dblink_exec('myconT',
      'insert into temp_student values ('
          || quote_nullable(rec.fname) || ','
          || quote_nullable(rec.lname) || ','
          || quote_nullable(rec.mname) || ','
          || quote_nullable(rec.address) || ')');
  END LOOP;
END;

Upvotes: 6

francs
francs

Reputation: 9219

Why not try it by yourself , according the error, you can try to solve them step by step !

Upvotes: -2

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