oracle pl sql CURSOR_ALREADY_OPEN

先创建表：

CREATE TABLE TB_USER
(
    ID INTEGER PRIMARY KEY,
    USER_NAME VARCHAR2(20) NOT NULL,
    USER_AGE INTEGER NOT NULL
);

CREATE SEQUENCE SEQ_USER
INCREMENT BY 1
START WITH 1
NOMAXVALUE
NOCYCLE
CACHE 10;

CREATE OR REPLACE TRIGGER TR_USER BEFORE INSERT ON TB_USER FOR EACH ROW
BEGIN
    SELECT SEQ_USER.NEXTVAL INTO :NEW.ID FROM DUAL;
END;

插入一些数据。

遍历数据：

DECLARE
V_AGE TB_USER.USER_AGE%TYPE;
V_NAME TB_USER.USER_NAME%TYPE;
CURSOR USER_CURSOR IS SELECT USER_NAME, USER_AGE FROM TB_USER;
BEGIN
  FOR USER_RECORD IN USER_CURSOR LOOP
    DBMS_OUTPUT.put_line(USER_RECORD.USER_NAME || ', ' || USER_RECORD.USER_AGE);
  END LOOP;
  EXCEPTION
    WHEN CURSOR_ALREADY_OPEN THEN
      DBMS_OUTPUT.put_line('cursor already open');
END;

执行上述代码，会显示每条记录。

FOR LOOP前不能OPEN，否则会报CURSOR_ALREADY_OPEN，错误代码如下：

DECLARE
V_AGE TB_USER.USER_AGE%TYPE;
V_NAME TB_USER.USER_NAME%TYPE;
CURSOR USER_CURSOR IS SELECT USER_NAME, USER_AGE FROM TB_USER;
BEGIN
  OPEN USER_CURSOR;--错误代码
  FOR USER_RECORD IN USER_CURSOR LOOP
    DBMS_OUTPUT.put_line(USER_RECORD.USER_NAME || ', ' || USER_RECORD.USER_AGE);
  END LOOP;
  EXCEPTION
    WHEN CURSOR_ALREADY_OPEN THEN
      DBMS_OUTPUT.put_line('cursor already open');
END;

上面OPEN了两次。