plsql - 匿名 block 内的更新失败但可以解决

Question

我有这个数据补丁:

ALTER TABLE MY_TABLE ADD new_id number;

DECLARE
  MAX_ID NUMBER;
BEGIN   
  SELECT max(id) INTO MAX_ID FROM some_table;
  EXECUTE IMMEDIATE 'CREATE sequence temp_seq start WITH ' || MAX_ID || ' increment by 1';
  UPDATE MY_TABLE SET new_id = temp_seq.nextval;
  EXECUTE IMMEDIATE 'DROP sequence temp_seq';  
END;
/

这给了我

UPDATE MY_TABLE SET new_id = temp_seq.nextval;
                                       *
ERROR at line 8:
ORA-06550: line 8, column 40:
PL/SQL: ORA-02289: sequence does not exist
ORA-06550: line 8, column 3:
PL/SQL: SQL Statement ignored

但是如果我将更新移到外面，它会起作用:

DECLARE
  MAX_ID NUMBER;
BEGIN   
  SELECT max(id) INTO MAX_ID FROM some_table;
  EXECUTE IMMEDIATE 'CREATE sequence temp_seq start WITH ' || MAX_ID || ' increment by 1';  
END;
/

UPDATE MY_TABLE SET new_id = temp_seq.nextval;

我可以使用第二种方法，但我很好奇为什么块内的更新失败。

Answer 1

因为在编译时该序列不存在。如果您想在 PL/SQL 块中使用它，您必须动态地这样做，就像您创建序列一样。