常用SQL/oracle循环语句

 

	常用SQL/oracle循环语句   标签： 常用SQL  oracle循环语句  分类： oracle数据库 2007-08-11 11:15   2、使用T-SQL标准控制结构：        1> 定义语句块        2> IF ... ELSE语句          3> IF EXISTS语句           语法：               declare               select @lname = ‘Smith’               if exists(select * from titles where au_lname = @lname)                  begin                     select @msg = ‘There are authors named’ + @lname                     print @msg                  end       4> 循环语句：           示例：               while @avg_price < ＄25 and (@count_rows < 10 or @max_price < ＄50)               begin                  select @avg_price          = avg(price) * 1.05,                         @max_price          = max(price) * 1.05,                         @time_thru_the_loop = @time_thru_the_loop + 1               end               if @time_thru_the_loop = 0                  select @time_thru_the_loop = 1               update titles                  set price = price * power(1.05, @time_thru_the_loop)          4> GOTO语句           语法：               GOTO label               ...               label:           示例：               begin transaction                  insert tiny(c1) values(1)                  if @@error != 0 goto error_handler                  commit transaction                  return               error_handler:                  rollback transaction                  return          5> RETURN语句           语法：               RETURN           （1）用于无条件退出一个批处理、存储过程或触发器。                示例：                    if not exists(select 1 from inventory                                   where item_num = @item_num)                    begin                       raiseerror 51345 ‘Not Found’                       return                    end                    print ‘No error found’                    return           （2）用于存储过程中返回状态值。                示例：                    create procedure titles_for_a_pub                           (@pub_name varchar(40) = null)                    as                    if @pub_name is null                       return 15                    if not exists(select 1 from publishers                                   where pub_name = @pub_name)                       return –101                    select t.tile from publishers p, titles t                     where p.pub_id = t.pub_id                       and pub_name = @pub_name                    return 0        2、使用PL/SQL标准控制结构：        1> 定义语句块           语法：               BEGIN                  Statements ；               END ；          2> IF ... THEN ... ELSE语句           语法：               IF boolean_expression THEN                  { statement | statement_block } ；               [ELSIF boolean_expression THEN      /*注意此处的写法—— ELSIF */                  { statement | statement_block } ；]               ...               [ELSE                  { statement | statement_block } ；]               END IF ；             示例：               v_NumberSeats rooms.number_seats%TYPE;               v_Comment VARCHAR2(35);               BEGIN                 SELECT number_seats                   INTO v_NumberSeats                   FROM rooms                  WHERE room_id = 99999;                 IF v_NumberSeats < 50 THEN                    v_Comment := 'Fairly small';                 ELSIF v_NumberSeats < 100 THEN                    v_Comment := 'A little bigger';                 ELSE                    v_Comment := 'Lots of room';                 END IF;               END;          3> 循环语句：          （1）简单循环语句：               语法：                   LOOP                      { statement | statement_block } ；                      [EXIT [WHEN condition] ；]                   END LOOP ；                   其中，语句EXIT [WHEN condition];等价于                       IF condition THEN                          EXIT ；                       END IF ；               示例1：                   v_Counter BINARY_INTEGER := 1;                   BEGIN                     LOOP                       -- Insert a row into temp_table with the current value of the                       -- loop counter.                       INSERT INTO temp_table                            VALUES (v_Counter, 'Loop index');                       v_Counter := v_Counter + 1;                       -- Exit condition - when the loop counter > 50 we will                       -- break out of the loop.                       IF v_Counter > 50 THEN                          EXIT;                       END IF;                     END LOOP;                   END;                 示例2：                   v_Counter BINARY_INTEGER := 1;                   BEGIN                     LOOP                       -- Insert a row into temp_table with the current value of the                       -- loop counter.                       INSERT INTO temp_table                            VALUES (v_Counter, 'Loop index');                       v_Counter := v_Counter + 1;                       -- Exit condition - when the loop counter > 50 we will                       -- break out of the loop.                       EXIT WHEN v_Counter > 50;                     END LOOP;                   END;            （2）WHILE循环语句：               语法：                   WHILE condition LOOP                      { statement | statement_block } ；                   END LOOP ；                 示例1：                   v_Counter BINARY_INTEGER := 1;                   BEGIN                     -- Test the loop counter before each loop iteration to                     -- insure that it is still less than 50.                     WHILE v_Counter <= 50 LOOP                       INSERT INTO temp_table                            VALUES (v_Counter, 'Loop index');                       v_Counter := v_Counter + 1;                     END LOOP;                   END;                 示例2：                   v_Counter BINARY_INTEGER;                   BEGIN                     -- This condition will evaluate to NULL, since v_Counter                     -- is initialized to NULL by default.                     WHILE v_Counter <= 50 LOOP                       INSERT INTO temp_table                            VALUES (v_Counter, 'Loop index');                       v_Counter := v_Counter + 1;                     END LOOP;                   END;            （3）数字式FOR循环语句：               语法：                   FOR loop_counter IN [REVERSE] low_bound..high_bound LOOP                      { statement | statement_block } ；                   END LOOP ；                   这里，loop_counter是隐式声明的索引变量。                 示例1：                   FOR循环的循环索引被隐式声明为BINARY_INTEGER。在循环前面没有                   必要声明它，如果对它进行了声明，那么循环索引将屏蔽外层的声明，                   如下所示                   v_Counter  NUMBER := 7;                   BEGIN                     -- Inserts the value 7 into temp_table.                     INSERT INTO temp_table (num_col)                       VALUES (v_Counter);                     -- This loop redeclares v_Counter as a BINARY_INTEGER, which                     -- hides the NUMBER declaration of v_Counter.                     FOR v_Counter IN 20..30 LOOP                       -- Inside the loop, v_Counter ranges from 20 to 30.                       INSERT INTO temp_table (num_col)                         VALUES (v_Counter);                     END LOOP;                     -- Inserts another 7 into temp_table.                     INSERT INTO temp_table (num_col)                       VALUES (v_Counter);                   END;                 示例2：                   如果在FOR循环中有REVERSE关键字，那么循环索引将从最大值向最                   小值进行循环。请注意语法是相同的——仍然首先书写的是最小值，                   如下所示                   BEGIN                     FOR v_Counter IN REVERSE 10..50 LOOP                           NULL;                     END LOOP;                   END;                 示例3：                   FOR循环中的最大值和最小值没有必要必须是数字型文字，它们可以                   是能够被转换为数字值的任何表达式，如下所示                   v_LowValue      NUMBER := 10;                   v_HighValue    NUMBER := 40;                   BEGIN                     FOR v_Counter IN REVERSE v_LowValue..v_HighValue LOOP                       INSER INTO temp_table                           VALUES (v_Counter, ‘Dynamically sqecified loop range’);                     END LOOP;                   END;          4> GOTO语句           语法：               GOTO label;               ...               <<label>>               ...             示例：               v_Counter  BINARY_INTEGER := 1;               BEGIN                 LOOP                   INSERT INTO temp_table                     VALUES (v_Counter, 'Loop count');                   v_Counter := v_Counter + 1;                   IF v_Counter > 50 THEN                     GOTO l_EndOfLoop;                   END IF;                 END LOOP;                               <<l_EndOfLoop>>                 INSERT INTO temp_table (char_col)                   VALUES ('Done!');               END;          5> EXIT语句           语法：               EXIT;           参见上面的PL/SQL标准控制结构之循环语句说明部分。