postgresql：使用游标从一个数据库中提取数据并将其插入到另一个数据库中

Question

这是使用游标的另一种算法，但我很难修复其错误...

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;

Answer 1

您很少需要在postgresql或pl / pgsql中显式使用游标。 您所写的内容看起来像是一个SQL Server游标循环构造，但您不必这样做。 另外，您可以使用“ PERFORM”而不是“ EXECUTE”来运行查询并丢弃结果：这将避免每次都重新解析查询（尽管它不能避免dblink每次都解析查询）。

您可以执行以下操作：

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;

Answer 2

为什么不自己尝试，根据错误，您可以尝试逐步解决它们！