如果在PLSQL块中没有做异常处理，在执行PLSQL块时，出现异常，会传递到调用环境，导致程序运行出错！
SCOTT@ prod> declare
2
3 v_ename emp.ename%type;
4 v_sal emp.sal%type;
5
6 begin
7
8 select ename,sal into v_ename,v_sal from emp where deptno=&n;
9
10 dbms_output.put_line(v_ename||':'||v_sal);
11
12
13 end;
1.预定义异常：
TOO_MANY_ROWS 在隐式游标处理时，select 返回行数超过一行
SQL> declare
2
3 v_ename emp.ename%type;
4 v_sal emp.sal%type;
5
6 begin
7
8 select ename,sal into v_ename,v_sal from emp where deptno=&n;
9
10 dbms_output.put_line(v_ename||':'||v_sal);
11
12 exception
13 when too_many_rows then
14 dbms_output.put_line('You return rows more than one !');
15 when others then
16 dbms_output.put_line('Other''s error !');
17 end;
2.NO_DATA_FOUND 在访问数据时，没有发现数据。
SQL> declare
2
3 v_ename emp.ename%type;
4 v_sal emp.sal%type;
5
6 begin
7
8 select ename,sal into v_ename,v_sal from emp where empno=#
9
10 dbms_output.put_line(v_ename||':'||v_sal);
11
12 exception
13 when no_data_found then
14 dbms_output.put_line('No data found ,Please input correct number !');
15 when others then
16 dbms_output.put_line('Other''s error !');
17 end;
3.ZERO_DIVIDE 除数为零
SQL> declare
2
3 v_num1 number :=10;
4 v_num2 number ;
5 v_num3 number;
6
7 begin
8 v_num2 := &nn;
9
10 v_num3 := v_num1 / v_num2 ;
11
12 dbms_output.put_line( 'Number is : '||v_num3);
13 exception
14 when zero_divide then
15 dbms_output.put_line( 'Divisor is equal to zero,Please input correct Number !');
16 when others then
17 dbms_output.put_line('Other''s error !');
18 end;