使用游标并在带有Java/JDBC的Oracle PL/SQL中获得结果 [英] Using cursors and getting result in Oracle PL/SQL with Java/JDBC

问题描述

我有一个像这样构造的PL/SQL查询:

I have a PL/SQL query constructed like this :

DECLARE
a NUMBER;
B NUMBER;
CURSOR cursor
IS
 ( SOME SELECT QUERY);
BEGIN
  OPEN cursor;
    LOOP
    SOME STUFF;
    END LOOP;
  CLOSE cursor;
END

如何使用jdbc从Java代码运行此查询并获取结果集?我尝试不使用游标来运行查询，并且其运行正常.我想不出一种在Java代码中执行此操作的方法.如果我直接将查询运行到oracle客户端上，它将正常工作.因此查询没有问题.

How can I run this query from a java code using jdbc and get the resultset? I have tried running the query without using cursor, and its running correctly. I couldn't figure out a way to do this in java code. If I run the query directly onto oracle client, it works with no problems. So there is no problem with the query.

P.S.由于某些限制，我不想将代码存储为存储过程并调用它.

P.S. I dont want to store the code as stored procedure and call that due to some constraints.

推荐答案

这是不可能的.您无法从匿名PL/SQL块返回结果集(因此无法从JDBC获取结果集).

This is not possible. You cannot return a result set from an anonymous PL/SQL block (and therefor there is no way to get it from JDBC).

您将需要直接从JDBC运行select.

You will need to run the select directly from JDBC.

唯一，非常丑陋的解决方法是使用dbms_output.put_line()，然后读取.但这是一个非常丑陋的技巧，直接在JDBC中处理SELECT查询的结果要好得多.

The only, really ugly workaround would be to use dbms_output.put_line() and the read that afterwards. But that is a really ugly hack and processing the result of the SELECT query directly in JDBC is much better.

这里是使用dbms_output的小例子:

Here is a little example using dbms_output:

Connection con = ....;

// turn on support for dbms_output
CallableStatement cstmt = con.prepareCall("{call dbms_output.enable(32000) }");
cstmt.execute();

// run your PL/SQL block
Statement stmt = con.createStatement();
String sql =
    "declare  \n" +
    " a number;  \n" +
    " cursor c1 is select id from foo;  \n" +
    "begin  \n" +
    "  open c1; \n" +
    "  loop \n" +
    "    fetch c1 into a;  \n" +
    "    exit when c1%notfound;  \n" +
    "    dbms_output.put_line('ID: '||to_char(a)); \n" +
    "  end loop; \n" +
    "end;";
stmt.execute(sql);

// retrieve the messages written with dbms_output
cstmt = con.prepareCall("{call dbms_output.get_line(?,?)}");
cstmt.registerOutParameter(1,java.sql.Types.VARCHAR);
cstmt.registerOutParameter(2,java.sql.Types.NUMERIC);

int status = 0;
while (status == 0)
{
    cstmt.execute();
    String line = cstmt.getString(1);
    status = cstmt.getInt(2);
    if (line != null && status == 0)
    {
        System.out.println(line);
    }
}

---

编辑2(对于评论来说太长了)

嵌套循环来检索数据几乎总是一个坏主意.如果您发现自己在做这样的事情:

---

Edit 2 (this is too long for a comment)

Nesting loops to retrieve data is almost always a bad idea. If you find your self doing something like this:

begin
  for data_1 in (select id from foo_1) loop
    dbms_output.put_line(to_char(data_1.id));

    for data_2 in (select f2.col1, f2.col2 from foo_2 f2 where f2.id = data_1.id) loop
        ... do something else
    end loop;

  end loop;
end;
/

这样做会更有效:

begin
  for data_1 in (select f2.col1, f2.col2 from foo_2 f2
                 where f2.id in (select f1.id from foo_1 f1)) loop

     ... do something

  end loop;
end;
/

使用以下类似的方法可以在JDBC中进行处理，而不会占用过多的内存:

This can be processed without an excessive memory in JDBC using something like this:

String sql = "select f2.col1, f2.col2 from foo_2 f2 where f2.id in (select f1.id from foo_1 f1)";
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(sql);
while (rs.next())
{
   String col1_value = rs.getString(1);
   int    col2_value = rs.getInt(2);
   ... do something
}

即使处理数十亿行，上述代码也只会在内存中保留一行.准确地说:JDBC驱动程序实际上将预取多行.默认值为10，可以更改.但是即使那样，您也不会占用过多的内存.

The above code will only hold one row in memory, even if you process billions of rows. To be precise: the JDBC driver will actually pre-fetch more than one row. The default is 10 and can be changed. But even then you don't have any excessive memory usage.

这篇关于使用游标并在带有Java/JDBC的Oracle PL/SQL中获得结果的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！