定义自定义异常引发它并查看它的来源

为了说明这一点，这里有一个具有 3 种不同错误行为的函数

• 参数完全是愚蠢的：我们使用用户定义的表达式
• 参数有拼写错误：我们使用 Oracle 标准 NO_DATA_FOUND 错误
• 另一个，但没有处理案件

随意适应你的标准：

DECLARE
  this_is_not_acceptable EXCEPTION;
  PRAGMA EXCEPTION_INIT(this_is_not_acceptable, -20077);
  g_err varchar2 (200) := 'to-be-defined';
  w_schema all_tables.OWNER%Type;

  PROCEDURE get_schema( p_table in Varchar2, p_schema out Varchar2)
  Is 
    w_err varchar2 (200) := 'to-be-defined';
  BEGIN
    w_err := 'get_schema-step-1:';
    If (p_table = 'Delivery-Manager-Is-Silly') Then
      raise this_is_not_acceptable;
    end if;
    w_err := 'get_schema-step-2:';
    Select owner Into p_schema 
      From all_tables
     where table_name like(p_table||'%');
  EXCEPTION
  WHEN NO_DATA_FOUND THEN
    -- handle Oracle-defined exception
     dbms_output.put_line('[WARN]'||w_err||'This can happen. Check the table name you entered.');
  WHEN this_is_not_acceptable THEN
    -- handle your custom error
     dbms_output.put_line('[WARN]'||w_err||'Please don''t make fun of the delivery manager.');
  When others then
     dbms_output.put_line('[ERR]'||w_err||'unhandled exception:'||sqlerrm);
     raise;    
  END Get_schema;  

BEGIN
  g_err := 'Global; first call:';
  get_schema('Delivery-Manager-Is-Silly', w_schema);
  g_err := 'Global; second call:';
  get_schema('AAA', w_schema);
  g_err := 'Global; third call:';
  get_schema('', w_schema);
  g_err := 'Global; 4th call:';
  get_schema('Can''t reach this point due to previous error.', w_schema);
  
EXCEPTION
  When others then
     dbms_output.put_line('[ERR]'||g_err||'unhandled exception:'||sqlerrm);
  -- you may raise this again to the caller if error log isn't enough.
--  raise;
END;
/

提供常规数据库：

[WARN]get_schema-step-1:Please don't make fun of the delivery manager.
[WARN]get_schema-step-2:This can happen. Check the table name you entered.
[ERR]get_schema-step-2:unhandled exception:ORA-01422: exact fetch returns more than requested number of rows
[ERR]Global; third call:unhandled exception:ORA-01422: exact fetch returns more than requested number of rows

请记住，例外处理罕见情况。我看到应用程序在每次访问时都会引发异常，只是为了询问用户密码，说没有连接……这么多的计算浪费。