PL/SQL6——异常处理(Exception)

 Exception是一种PL/SQL标识符，当运行的PL/SQL块出现错误或警告，则会触发异常处理。为了提高程序的健壮性，可以在PL/SQL块中引
入异常处理部分，进行捕捉异常，并根据异常出现的情况进行相应的处理。
 
一、异常的类型 
    ORACLE异常分为两种类型：系统异常、自定义异常。
    其中系统异常又分为：预定义异常和非预定义异常。
 
    1.预定义异常
        ORACLE定义了他们的错误编号和异常名字，常见的预定义异常处理Oracle常见的错误
   
        NO_DATA_FOUND          SELECT ... INTO ... 时，没有找到数据
        DUL_VAL_ON_INDEX       试图在一个有惟一性约束的列上存储重复值
        CURSOR_ALREADY_OPEN    试图打开一个已经打开的游标
        TOO_MANY_ROWS          SELECT ... INTO ... 时，查询的结果是多值
        ZERO_DIVIDE            零被整除
 
    2.非预定义异常
        ORACLE为它定义了错误编号，但没有定义异常名字。我们使用的时候，先声名一个异常名，
        通过伪过程PRAGMA EXCEPTION_INIT，将异常名与错误号关联起来。
 
    3.自定义异常
        程序员从我们业务角度出发，制定的一些规则和限制。
 
二、异常处理
    PL/SQL中，异常处理按个步骤进行：
        定义异常
        抛出异常
        捕获及处理异常
 
    a.定义异常
        exception_name EXCEPTION;
 
    b.抛出异常
        RAISE exception_name
 
    c.捕获及处理异常
        EXCEPTION
            WHEN e_name1 [OR e_name2 ... ] THEN
                statements;
            WHEN e_name3 [OR e_name4 ... ] THEN
                statements;
                ......
            WHEN OTHERS THEN
                statements;
        END;
        /
 
 
三、异常处理示例   
    1.预定义异常的例子
        --演示一个整除的异常
            DECLARE
                v_n1 NUMBER:=50;
                v_n2 NUMBER:=0;
                v_n3 NUMBER;
            BEGIN
                v_n3:=v_n1/v_n2;
                DBMS_OUTPUT.PUT_LINE('v_n3='||v_n3);
            EXCEPTION
                WHEN ZERO_DIVIDE  THEN
                    DBMS_OUTPUT.PUT_LINE('v_n2 don't is 0');       
            END;
            /
       
        --演示VALUE_ERROR(错误号ORA-06502)
            scott@ORCL> declare
              2  v_ename varchar2(3);
              3  begin
              4      select ename into v_ename from emp where empno=&eno;
              5      dbms_output.put_line(v_ename);
              6  exception
              7      when value_error then
              8      dbms_output.put_line('variable datatype length is small');
              9  end;
             10  /
            Enter value for eno: 7788
            old   4:     select ename into v_ename from emp where empno=&eno;
            new   4:     select ename into v_ename from emp where empno=7788;
            variable datatype length is small
 
            PL/SQL procedure successfully completed.       
       
        --演示TOO_MANY_ROWS(对应Oracle错误号ORA-01422)
            scott@ORCL> declare
              2  v_ename emp.ename%type;
              3  begin
              4      select ename into v_ename from emp where deptno=&dno;
              5  exception
              6      when too_many_rows then
              7      dbms_output.put_line('Too many rows are returned');
              8  end;
              9  /
            Enter value for dno: 10
            old   4:     select ename into v_ename from emp where deptno=&dno;
            new   4:     select ename into v_ename from emp where deptno=10;
            Too many rows are returned
 
            PL/SQL procedure successfully completed.           
       
    2.非预定义异常
        非预定义异常使用的基本过程
            a.定义一个异常名
            b.将异常名与异常编号相关联
            c.在异常处理部分捕捉并处理异常
       
        DECLARE
            e_deptid EXCEPTION;
            PRAGMA EXCEPTION_INIT(e_deptid,-2292);
        BEGIN
            DELETE FROM DEPT WHERE DEPTNO=10;
        EXCEPTION
            WHEN e_deptid THEN
                DBMS_OUTPUT.PUT_LINE('at sub table have record!');
        END;
        /
 
        DECLARE
            e_emp EXCEPTION;
            PRAGMA EXCEPTION_INIT(e_emp,-2291);
        BEGIN
            INSERT INTO EMP(empno,deptno) VALUES (7935,60);
        EXCEPTION
            WHEN e_emp THEN
                DBMS_OUTPUT.PUT_LINE('60 at table dept not exist');
        END;
        /  
 
    3.自定义异常
        自定义异常与Oracle错误没有任何关系，有开发人员为特定情况所定义的例外
        下面的例子中当输入empno为时，尽管该雇员编号不存在，但PL/SQL代码并未给出适当的提示
            scott@ORCL> declare
              2  e_integrity exception;
              3  pragma exception_init(e_integrity,-2291);
              4  begin
              5      update emp set deptno=&dno where empno=&eno;
              6  exception
              7      when e_integrity then
              8      dbms_output.put_line('The dept is not exists');
              9  end;
             10  /
            Enter value for dno: 20
            Enter value for eno: 1111
            old   5:     update emp set deptno=&dno where empno=&eno;
            new   5:     update emp set deptno=20 where empno=1111;
 
            PL/SQL procedure successfully completed.
 
        针对上述情况，可以使用自定义异常处理。
        对于自定义的异常处理需要显示的触发，其步骤如下
            a.定义异常(在declare部分进行定义)
            b.显示触发异常(在执行BEGIN部分触发异常，使用RAISE语句)
            c.引用异常(在EXCEPTION部分捕捉并处理异常)
       
        --对上面的例子，使用自定义异常来处理，代码如下：
            scott@ORCL> declare
              2  e_integrity exception;
              3  pragma exception_init(e_integrity,-2291);
              4  e_no_employee exception;
              5  begin
              6      update emp set deptno=&dno where empno=&eno;
              7      if sql%notfound then
              8          raise e_no_employee;
              9      end if;
             10  exception
             11      when e_integrity then
             12          dbms_output.put_line('The dept is not exists');
             13      when e_no_employee then
             14          dbms_output.put_line('The employee is not exists');
             15  end;
             16  /
            Enter value for dno: 20
            Enter value for eno: 1234
            old   6:     update emp set deptno=&dno where empno=&eno;
            new   6:     update emp set deptno=20 where empno=1234;
            The employee is not exists
 
            PL/SQL procedure successfully completed.       
       
        --下面的例子中，如果插入的工资少于，就抛出异常
            DECLARE
                v_sal emp.sal%TYPE;
                v_id emp.empno%TYPE;
                e_sal EXCEPTION;      --定义异常
            BEGIN
                v_id:=&inputid;
                v_sal:=&inputsal;
                INSERT INTO emp (empno,sal) VALUES (v_id,v_sal);
                IF v_sal<700 THEN
                    RAISE e_sal;      --捕捉异常
                END IF;
            EXCEPTION                 --处理异常
                WHEN e_sal THEN
                    ROLLBACK;
                    DBMS_OUTPUT.PUT_LINE('Sal must be more than 700'); 
            END;
            /
           
四、使用异常函数处理异常           
    1.SQLCODE与SQLERRM函数
        函数SQLCODE用于取得Oracle错误号
        函数SQLERRM用于取得与错误号对应的相关错误消息
            scott@ORCL> get /u01/bk/scripts/sqlcode_errm.sql
              1  undef v_sal
              2  declare
              3      v_ename emp.ename%type;
              4      begin
              5          select ename into v_ename from emp
              6          where sal=&&v_sal;
              7          dbms_output.put_line('Employee Name:'||v_ename);
              8  exception
              9      when no_data_found then
             10          dbms_output.put_line('The employee is not exists for salary '||&v_sal);
             11      when others then
             12          dbms_output.put_line('Error No:'||SQLCODE);
             13          dbms_output.put_line(SQLERRM);
             14* end;
            scott@ORCL> start /u01/bk/scripts/sqlcode_errm.sql
            Enter value for v_sal: 1600
            old   5:         where sal=&&v_sal;
            new   5:         where sal=1600;
            old   9:         dbms_output.put_line('The employee is not exists for salary '||&v_sal);
            new   9:         dbms_output.put_line('The employee is not exists for salary '||1600);
            Error No:-1422
            ORA-01422: exact fetch returns more than requested number of rows
 
            PL/SQL procedure successfully completed.   
 
    2.RAISE_APPLICATION_ERROR
        是将应用程序专有的错误从服务器端转达到客户端应用程序(其他机器上的SQLPLUS或者其他前台开发语言)。
        该函数用于在PL/SQL中定义错误消息，且只能在数据库端的子程序中使用(存储过程、函数、包、触发器)，不能在匿名块和客户端的
        子程序中使用
 
        使用方法
            RAISE_APPLICATION_ERROR(error_number,message[,{true | false}]);
           
            该函数内的错误代码和内容，都是用用户自定义
            error_number：用于定义错误号，且错误号从-20000 到-20999 之间，以避免与ORACLE 的任何错误代码发生冲突。
            message：用于指定错误消息，且消息长度不能超过k，超出部分将被截取
            可选参数true,false:默认值为false，会替换先前的所有错误。当设置为true，则该错误会被放在先前错误堆栈中。
           
            scott@ORCL> get /u01/bk/scripts/sp_raise_comm.sql
              1  create or replace procedure raise_comm
              2  (v_no emp.empno%type,v_comm out emp.comm%type)
              3  as
              4  begin
              5       select comm into v_comm from emp where empno=v_no;
              6       if v_comm is null then
              7           raise_application_error(-20001,'It is no comm for this employee');
              8       end if;
              9  exception
             10       when no_data_found then
             11       dbms_output.put_line('The employee is not exist');
             12* end;
            scott@ORCL> start /u01/bk/scripts/sp_raise_comm.sql
 
            Procedure created.
 
            scott@ORCL> variable g_sal number;
            scott@ORCL> call raise_comm(7788,:g_sal);
            call raise_comm(7788,:g_sal)
                 *
            ERROR at line 1:
            ORA-20001: It is no comm for this employee
            ORA-06512: at "SCOTT.RAISE_COMM", line 7
                       
            scott@ORCL> call raise_comm(7499,:g_sal);
 
            Call completed.
 
            scott@ORCL> print g_sal
 
                 G_SAL
            ----------
                   300     
 
五、PL/SQL编译警告
    1.PL/SQL警告的分裂
        SEVERE: 用于检查可能出现的不可预料结果或错误结果,例如参数的别名问题.
        PERFORMANCE: 用于检查可能引起性能问题,如在INSERT操作是为NUMBER列提供了VARCHAR2类型数据.
        INFORMATIONAL: 用于检查程序中的死代码.
        ALL: 用于检查所有警告.
   
    2.控制PL/SQL警告消息
        通过设置初始化参数PLSQL_WARNINGS来启用在编译PL/SQL子程序时发出警告消息，缺省为DISABLE:ALL
        警告消息设置的级别
            系统级别
            会话级别
            ALTER PROCEDURE
            既可以激活或禁止所有警告类型,也可以激活或禁止特定消息号
            scott@ORCL> show parameter plsql%ings;
 
            NAME                                 TYPE        VALUE
            ------------------------------------ ----------- ------------------------------
            plsql_warnings                       string      DISABLE:ALL       
           
            scott@ORCL> ALTER SYSTEM SET PLSQL_WARNINGS='ENABLE:ALL' |'DISABLE:ALL'
            scott@ORCL> ALTER SESSION SET PLSQL_WARNINGS='ENABLE:PERFORMANCE' |'DISABLE:ALL'
            scott@ORCL> ALTER PROCEDURE usp COMPILE PLSQL_WARNINGS='ENABLE:PERFORMANCE';
            scott@ORCL> ALTER SESSION SET PLSQL_WARNINGS='ENABLE:SEVERE','DISABLE:PERFORMANCE','ERROR:06002';
   
    3.演示PL/SQL编译告警
        a.检测死代码
            在下面的代码中，ELSE子句永远不会执行,应该避免出现类似的死代码.
            从Oracle 10g开始,在编写PL/SQL子程序之前开发人员可以激活警告检查.
           
                scott@ORCL> get /u01/bk/scripts/dead_code.sql
                  1  CREATE OR REPLACE PROCEDURE dead_code AS
                  2     x number := 10;
                  3  BEGIN
                  4     IF x>0 THEN
                  5             x:=1;
                  6     ELSE             
                  7             x:=2;    --死代码
                  8     END IF;
                  9* END dead_code;
               
                scott@ORCL> start /u01/bk/scripts/dead_code.sql
               
                scott@ORCL> alter session set plsql_warnings='enable:informational';
               
                scott@ORCL> show parameter plsql%ings
 
                NAME                                 TYPE        VALUE
                ------------------------------------ ----------- ------------------------------
                plsql_warnings                       string      ENABLE:INFORMATIONAL, DISABLE:
                                                                 PERFORMANCE, DISABLE:SEVERE
                                                                 
                scott@ORCL> alter procedure dead_code compile;
 
                SP2-0805: Procedure altered with compilation warnings          
 
                scott@ORCL> show errors;
                Errors for PROCEDURE DEAD_CODE:
 
                LINE/COL ERROR
                -------- -----------------------------------------------------------------
                4/6      PLW-06002: Unreachable code
                7/3      PLW-06002: Unreachable code
       
        b.检测引起性能问题的代码
            scott@ORCL> create or replace procedure update_sal
              2  (no number,salary varchar2)
              3  as
              4  begin
              5      update emp set sal=salary where empno=no;
              6  end;
              7  /
 
            Procedure created.
 
            scott@ORCL> alter session set plsql_warnings='enable:performance';
 
            scott@ORCL> alter procedure update_sal compile;
 
            SP2-0805: Procedure altered with compilation warnings
 
            scott@ORCL> show errors
            Errors for PROCEDURE UPDATE_SAL:
 
            LINE/COL ERROR
            -------- -----------------------------------------------------------------
            5/24     PLW-07202: bind type would result in conversion
away from column