DECLARE
  qty_on_hand NUMBER(5);    --声明部分定义变量、游标和自定义异常
BEGIN     --begin到end 包含 SQL 和 PL/SQL 语句的可执行部分
  SELECT quantity INTO qty_on_hand
  FROM Products
  WHERE product = ‘芭比娃娃‘
  FOR UPDATE OF quantity;
  IF qty_on_hand > 0 THEN
    UPDATE Products SET quantity = quantity + 1
    WHERE product = ‘芭比娃娃‘;
    INSERT INTO purchase_record
    VALUES (‘已购买芭比娃娃‘, SYSDATE);
  END IF;
  COMMIT;
EXCEPTION  /* 异常处理语句 */  --指定出现错误时需要执行的操作
  WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE(‘出错:‘|| SQLERRM);  
END;

identifier [CONSTANT] datatype [NOT NULL]   
        [:= | DEFAULT expr];

DECLARE
  icode VARCHAR2(6);
  p_catg VARCHAR2(20);
  p_rate NUMBER;
  c_rate CONSTANT NUMBER := 0.10;
BEGIN
  ...
  icode := ‘i205‘;
  SELECT p_category, itemrate * c_rate
  INTO  p_catg, p_rate
  FROM itemfile WHERE itemcode = icode;
  ...
END;

SET SERVEROUTPUT ON
DECLARE
  clob_var   CLOB;
  amount     INTEGER;
  offset     INTEGER;
  output_var VARCHAR2(100);
BEGIN
  SELECT chapter_text INTO clob_var   --从表中选择 CLOB 定位符到 clob_var变量中
  FROM my_book_text
  WHERE chapter_id=5;
  amount := 24;  -- 要读取的字符数
  offset := 1;   -- 起始位置
  DBMS_LOB.READ(clob_var,amount,offset,output_var);  --从CLOB数据中读取24个字符存储到 output_var 变量中
  DBMS_OUTPUT.PUT_LINE(output_var);  --显示读到的信息
END;

icode itemfile.itemcode%TYPE;
emp_rec scott.emp%ROWTYPE;

DECLARE
    icode VARCHAR2(4);
    irate NUMBER;
BEGIN
    icode := ‘i203‘;
  SELECT itemrate INTO irate FROM itemfile 
  WHERE  itemcode = icode;
  IF irate > 200 THEN      --条件判断
    UPDATE itemfile SET itemrate = itemrate - 200
    WHERE itemcode = icode;
  ELSE
    UPDATE itemfile SET itemrate = itemrate - 50
    WHERE itemcode = icode;
  END IF;    --结束
  DBMS_OUTPUT.PUT_LINE(‘itemrate=‘|| irate);
END;

BEGIN
    CASE ‘&grade’
      WHEN ’A’ THEN DBMS_OUTPUT.PUT_LINE(’优异’);
      WHEN ’B’ THEN DBMS_OUTPUT.PUT_LINE (优秀’);
      WHEN ’C’ THEN DBMS_OUTPUT.PUT_LINE (’良好’);
      WHEN ’D’ THEN DBMS_OUTPUT.PUT_LINE (’一般’);
      WHEN ’F’ THEN DBMS_OUTPUT.PUT_LINE (’较差’);
      ELSE DBMS_OUTPUT.PUT_LINE (’没有此成绩’);
    END CASE;
END;

FOR counter IN [REVERSE] value1..value2
LOOP 
  sequence_of_statements
END LOOP;

loop
  循环体；
  exit when循环条件;
end loop

while 条件
loop
  执行语句段;
end loop;

--while循环
--循环输出Hello world
declare
    var_i int := 10;
begin
    loop
        dbms_output.put_line(‘Hello world‘);
        if var_i = 0 then
            exit;
        end if;
        var_i := var_i - 1;
    end loop;
end;

--loop输出1-10
declare
    var_i int := 1;
begin
    loop
        dbms_output.put_line(‘i = ‘ || var_i);
        exit when var_i = 10;
        var_i := var_i + 1;
    end loop;
End

--while循环1-5
Declare
    var_i int:=1;
Begin
    while var_i<=10 loop
        Dbms_output.put_line(‘I=‘||var_i);
        Var_i:=var_i+1;
    End loop;
End;



--for 循环 : for 变量 in 范围 loop
--1-10输出
begin
    for i in 1..10 loop
        dbms_output.put_line(‘i = ‘ || i);
    end loop;
end

--对员工的工资判断，如果少于2000则加50，直到工资满足为止！
declare
    var_sal int;
begin
    loop
        select sal into var_sal from emp where empno = 7499;
        exit when var_sal >= 2000;
        update emp set sal = sal + 50 where empno = 7499;
        dbms_output.put_line(‘加50‘);
    end loop;
end;

   EXECUTE IMMEDIATE dynamic_sql_string

      [INTO  define_variable_list]

      [USING bind_argument_list];

DECLARE
  sql_stmt VARCHAR2(200);
  emp_id NUMBER(4) := 7566;
  emp_rec emp%ROWTYPE;
BEGIN
    EXECUTE IMMEDIATE 
    ‘CREATE TABLE bonus1 (id NUMBER, amt NUMBER)‘;

    sql_stmt := ‘SELECT * FROM emp WHERE empno = :id‘;
    EXECUTE IMMEDIATE sql_stmt INTO emp_rec USING emp_id;
END;

--显示员工编号为7499的所有信息
declare
    Var_row emp%rowtype;
begin
    select * into var_row from emp where empno = 7499;
    dbms_output.put_line(‘编号=‘ || var_row.empno || ‘姓名=‘ || var_row.ename);
end;

--动态执行
declare
    var_row emp%rowtype;
    var_sql varchar(100);
    var_empno int;
begin
    var_sql := ‘select * from emp where empno = :num‘ ;
    execute immediate var_sql into var_row using var_empno;
    dbms_output.put_line(‘编号=‘ || var_row.empno || ‘姓名=‘ || var_row.ename);
end;

--用动态SQL来实现分页
begin
    execute immediate ‘select * from (select rownum rn, d.* from (select * from :tableName order by sal desc) d) where rn > :min and rn <= :max‘ using ‘emp‘ , 1, 5;
End;

access_into_null   --在未初化对象时出现
case_not_found    --在CASE语句中的选项与用户输入的数据不匹配时出现
collection_is_null    --在给尚未初始化的表或数组赋值时出现
cursor_already_open    --在用户试图打开已经打开的游标时出现
dup_val_on_index    --在用户试图将重复的值存在使用唯一索引的数据库列中时出现
invalid_cursor        --在执行非法游标运算（如打开一个尚未打开的游标）时出现
invalid_number     --在将字符串转换为数字时出现
login_denied        --在输入的用户名或密码无效时出现
no_data_found     --在表中不存在的请求的行时出现，此外，当程序引用已经删除的元素时
storage_error       --在内存损坏或PL/SQL耗尽内存时出现
too_many_rows    --在执行SELECT INTO语句后返回多行时出现
value_error    --在产生大小限制错误时出现
zero_divide    --以零作除数时出现
Others          --针对所有异常

DECLARE 
  invalidCATEGORY EXCEPTION;
  category VARCHAR2(10);
BEGIN
  category := ‘&Category‘;
  IF category NOT IN (‘附件‘,‘顶盖‘,‘备件‘) THEN
    RAISE invalidCATEGORY;
  ELSE
    DBMS_OUTPUT.PUT_LINE(‘您输入的类别是‘|| category);
  END IF;
EXCEPTION
  WHEN invalidCATEGORY THEN
    DBMS_OUTPUT.PUT_LINE(‘无法识别该类别‘);
END;

DECLARE
  rate itemfile.itemrate%TYPE;
  rate_exception EXCEPTION;  --定义异常
BEGIN
  SELECT NVL(itemrate,0) INTO rate FROM itemfile 
  WHERE  itemcode = ‘i207‘;
  IF rate = 0 THEN
    RAISE rate_exception;  --引发异常
  ELSE
    DBMS_OUTPUT.PUT_LINE(‘项费率为：‘ || rate);
  END IF;
EXCEPTION
  WHEN rate_exception THEN  --扑捉异常
    RAISE_APPLICATION_ERROR(-20001, ‘未指定项费率‘);
END;

begin
    if 10 > 5 then
        raise_application_error(-20001, ‘这个是自定义错误显示‘);
    end if;
end;