set serveroutput on;

declare

    cursor cemp is select to_char(hiredate, 'yyyy') from emp;

    phiredate varchar2(4);

    count80 number := 0;

    count81 number := 0;

    count82 number := 0;

    count87 number := 0;

begin

    open cemp;

    loop

        fetch cemp into phiredate;

        exit when cemp%notfound;

        if phiredate='1980' then count80:=count80+1;

        elsif phiredate='1981' then count81:=count81+1;

        elsif phiredate='1982' then count82:=count82+1;

        else count87 := count87 + 1;

        end if; 

    end loop;

    close cemp;

    dbms_output.put_line('Total '||count80 + count81 + count82 + count87);

    dbms_output.put_line('1980 '||count80);

    dbms_output.put_line('1981 '||count81);

    dbms_output.put_line('1982 '||count82);

    dbms_output.put_line('1987 '||count87);

end;

/

错误报告 -

ORA-06502: PL/SQL: 数字或值错误 :  字符到数值的转换错误

ORA-06512: 在 line 20

06502. 00000 -  "PL/SQL: numeric or value error%s"

*Cause:    An arithmetic, numeric, string, conversion, or constraint error

           occurred. For example, this error occurs if an attempt is made to

           assign the value NULL to a variable declared NOT NULL, or if an

           attempt is made to assign an integer larger than 99 to a variable

           declared NUMBER(2).

*Action:   Change the data, how it is manipulated, or how it is declared so

           that values do not violate constraints.