IF EXISTS 条件不适用于 PLSQL

问题描述

我试图在条件为真时打印文本.选择代码完全正常.当我只运行选择代码时，它显示 403 值.但是当条件存在时我必须打印一些文本.以下代码有什么问题.

I am trying to print the TEXT when condition is TRUE. The select code is perfectly working fine. It's showing 403 value when i only run select code. But I have to print some text when condition exists. What's the problem with following code.

BEGIN
IF EXISTS(
SELECT CE.S_REGNO FROM
COURSEOFFERING CO
JOIN CO_ENROLMENT CE
  ON CE.CO_ID = CO.CO_ID
WHERE CE.S_REGNO=403 AND CE.COE_COMPLETIONSTATUS = 'C' AND CO.C_ID = 803
)
THEN
    DBMS_OUTPUT.put_line('YES YOU CAN');
END;

错误报告如下:

Error report:
ORA-06550: line 5, column 1:
PLS-00103: Encountered the symbol "JOIN" when expecting one of the following:

   ) , with group having intersect minus start union where
   connect
06550. 00000 -  "line %s, column %s:
%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:

推荐答案

IF EXISTS() 在语义上不正确.EXISTS 条件只能在 SQL 语句中使用.因此，您可以按如下方式重写 pl/sql 块:

IF EXISTS() is semantically incorrect. EXISTS condition can be used only inside a SQL statement. So you might rewrite your pl/sql block as follows:

declare
  l_exst number(1);
begin
  select case 
           when exists(select ce.s_regno 
                         from courseoffering co
                         join co_enrolment ce
                           on ce.co_id = co.co_id
                        where ce.s_regno=403 
                          and ce.coe_completionstatus = 'C' 
                          and ce.c_id = 803
                          and rownum = 1
                        )
           then 1
           else 0
         end  into l_exst
  from dual;

  if l_exst = 1 
  then
    DBMS_OUTPUT.put_line('YES YOU CAN');
  else
    DBMS_OUTPUT.put_line('YOU CANNOT'); 
  end if;
end;

或者你可以简单地使用count函数来确定查询返回的行数，以及rownum=1谓词——你只需要知道一条记录是否存在:

Or you can simply use count function do determine the number of rows returned by the query, and rownum=1 predicate - you only need to know if a record exists:

declare
  l_exst number;
begin
   select count(*) 
     into l_exst
     from courseoffering co
          join co_enrolment ce
            on ce.co_id = co.co_id
    where ce.s_regno=403 
      and ce.coe_completionstatus = 'C' 
      and ce.c_id = 803
      and rownum = 1;

  if l_exst = 0
  then
    DBMS_OUTPUT.put_line('YOU CANNOT');
  else
    DBMS_OUTPUT.put_line('YES YOU CAN');
  end if;
end;

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