oracle - PL/SQL << word >>是什么意思

PL/SQL中双尖括号中单词的含义是什么，例如。 <<word>>？

我试图进行谷歌搜索，但谷歌跳过标点符号。

它是干什么用的？

最佳答案

正如问题评论者提到的那样，它用于标记复合语句，也用作GOTO的目标。您可以使用END和END LOOP中的标签，这对于提高可读性非常有用，例如<<countdown>> for i in 1.9 loop blah; end loop countdown;
这是一个例子:

set echo on
set serveroutput on

<<begin_end_block>>
declare
  msg varchar2(1000);
begin
  dbms_output.enable;
  msg := chr(9) || 'start';
  <<loopblk>>
  for itr8 in 1 .. 5
  loop
    msg := msg || chr(10) || chr (9) ||  'loop';
    dbms_output.put_line ('Iterator is ' || itr8);
    <<ifblck>> if itr8 > 2
    then
      msg := msg || chr(10) || chr(9) || 'greater than 2';
      goto gototarg;
    end if;
    exit loopblk when mod (itr8, 4) = 0;
    continue loopblk;
    <<gototarg>>
    dbms_output.put_line ('after goto target');
  end loop loopblk;
  dbms_output.put_line ('Ending, here are the messages' || chr(10) || msg);
end begin_end_block;
/

输出为:

anonymous block completed
Iterator is 1
Iterator is 2
Iterator is 3
after goto target
Iterator is 4
after goto target
Iterator is 5
after goto target
Ending, here are the messages
    start
    loop
    loop
    loop
    greater than 2
    loop
    greater than 2
    loop
    greater than 2