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常用SQL/oracle循环语句
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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 < $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_seatsINTO 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;
...
<
...
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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