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常用SQL/oracle循环语句

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Jun 07, 2016 pm 03:44 PM

oraclesqluseCommonly usedcyclestatement

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 en

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

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)

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

v_Comment := 'Fairly small';

ELSIF v_NumberSeats

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

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

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;

...

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;

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。

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