Question

这是使用光标的另一种算法，但我很难修复它的错误......

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。您编写的内容看起来很像SQL Server游标循环结构，您不需要这样做。此外，您可以使用“PERFORM”而不是“EXECUTE”来运行查询并丢弃结果：这将避免每次重新解析查询（尽管每次都无法避免dblink解析查询）。

你可以做更多这样的事情：

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

为什么不亲自尝试，根据错误，你可以尝试一步一步解决它们！

postgresql：USING CURSOR用于从一个数据库中提取数据并将它们插入另一个数据库

2 个答案: