错误:引用计数器作为分配目标-PL/SQL [英] ERROR: Reference the counter as the target of an assignment - PL/SQL

问题描述

我对SQL比较陌生. 我正在尝试通过这段代码打印一个简单的图案

I'm relatively new to SQL. I'm trying to print a simple pattern through this code

declare
   n number(2):=5;
   temp number(2):=n;
 begin
   for a in 1..5
       a:=a+1;loop
       for b in 1..temp loop
           b:=b+1;
           dbms_output.put_line(' ');
           temp:=temp-1;
       end loop;
   for c in 1..2*a-1 loop
   c:=c+1;
   dbms_output.put_line('*');
 end loop;
end loop;
end;
/

我不断收到此错误:

PLS-00103: Encountered the symbol "A" when expecting one of the following:
* & - + / at loop mod remainder rem <an exponent (**)> ||
multiset

我知道Oracle不允许将计数器作为分配的目标，这就是为什么我在第6行不断出现错误的原因，但是即使声明另一个全局变量并在其中分配增量语句，也无法使它工作它，但也不起作用. 请帮忙. 谢谢！

I understand Oracle doesn't allow to reference the counter as the target of an assignment which is why I keep getting error at line 6 but I'm unable to make it work even by declaring another global variable and assigning increment statement in it but it doesn't work either. Please help. Thanks!

推荐答案

修改先前的答案，实际上是给您Pascal的三角形，您曾提到您尝试在评论中添加它:

Modifying the previous answers to actually give you Pascal's triangle, which you mentioned you were attempting in a comment:

set serveroutput on format wrapped
declare
   n number(2):=5;
begin
  for a in 1..n loop
    for b in 1..n-a loop
      dbms_output.put(' ');
    end loop;
    for c in 1..2*a-1 loop
      dbms_output.put('*');
    end loop;
    dbms_output.new_line;
  end loop;
end;
/

    *
   ***
  *****
 *******
*********

PL/SQL procedure successfully completed.

您的两个dbms_output.put_line调用都只需为dbms_output.put，因为这是将每个*单独打印在一行上.但是您确实需要在每次a循环之后都进行换行，因此我在此末尾添加了dbms_output.newline.您还在b循环内减小temp，这意味着在a循环周围第二次为(n-1)而不是零.但实际上您根本不需要单独的temp变量，因为该变量始终与(n-a)+1相同，并且+1只是在每行上都留有多余的空间. (我假设您只想稍后在某个位置更改n的值，所以我也创建了a循环1..n).使用n := 8:

Both your dbms_output.put_line calls needed to be just dbms_output.put, as that was printing each * on a line on its own. But you do need a line break after each time around the a loop, so I've added a dbms_output.newline at the end of that. You were also decrementing temp inside the b loop, which meant it was zero instead of (n-1) for the second time around the a loop; but you don't really need a separate temp variable at all as that is always the same as (n-a)+1 and the +1 just puts an extra space on every line. (I also made the a loop 1..n as I assume you want to change the value of n later in one place only). With n := 8:

       *
      ***
     *****
    *******
   *********
  ***********
 *************
***************

重要的是，尽管您也必须set serveroutput on format wrapped，否则将丢弃在b循环中生成的前导空格.

Crucially though you also have to set serveroutput on format wrapped, otherwise the leading spaces you're generating in the b loop are discarded.

您也可以在普通SQL中执行此操作，尽管您需要提供两次5或使用绑定或替换变量:

You can also do this in plain SQL, though you need to supply the 5 twice, or use a bind or substitution variable:

select lpad(' ', 5 - level, ' ') || rpad('*', (level * 2) - 1, '*') as pascal
from dual
connect by level <= 5

PASCAL
------------------------------
    *
   ***
  *****
 *******
*********

您的b和c循环实际上只是在手动执行lpad.

Your b and c loops are just doing a manual lpad really.

这篇关于错误:引用计数器作为分配目标-PL/SQL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！