触发器、游标
一、触发器
触发器的两张虚拟表:
Tickets表原始数据：
TicketsOrders表原始数据：
1.插入触发器
创建：
1
create
trigger
ticketsOrdersInsert
2
on
edisondb..ticketsOrders
3
after
insert
4
as
5
begin
6
if
(
select
t.currentAmount
from
tickets
as
t,inserted
7
where
t.ticketid
=
inserted.ticketid)
<
8
(
select
amount
from
inserted)
9
begin
10
print
'
订票数超过库存数，无法订票！
'
11
rollback
transaction
--
---将插入操作进行回滚
12
end
13
else
14
print
'
订票成功！
'
15
update
tickets
set
tickets.currentAmount
=
tickets.currentAmount
-
inserted.amount
16
from
inserted
17
where
tickets.ticketid
=
inserted.ticketid
18
end
插入非法值：
1
use
edisondb;
2
3
insert
into
ticketsOrders(custid ,ticketid ,amount)
4
values
(
10001
,
1
,
100
);
2.更新触发器
创建：
1
create
trigger
ticketsUpdate
2
on
edisondb..Tickets
3
after
update
4
as
5
begin
6
if
update
(totalAmount)
7
begin
8
if
(
select
totalAmount
from
deleted)
<>
(
select
currentAmount
from
deleted)
9
begin
10
raiserror
(
'
该票已经有人订票，不可更新总票数
'
,
16
,
1
)
11
rollback
transaction
--
--回滚
12
end
13
end
14
end
1
use
edisondb;
2
update
Tickets
set
tickets.totalAmount
=
100
3
where
ticketid
=
1
;
3.删除触发器
创建：
1
create
trigger
ticketsDelete
2
on
edisondb..Tickets
3
after
delete
4
as
5
begin
6
if
(
select
totalAmount
from
deleted)
<>
(
select
currentAmount
from
deleted)
7
begin
8
print
'
该票已经有人订购，不可删除
'
9
rollback
transaction
--
--回滚
10
end
11
end
1
use
edisondb;
2
delete
from
tickets
3
where
ticketid
=
1
;
二、游标
游标：行级操作，性能杀手
SQL查询：数据集操作，速度快（优先选用）
使用游标进行操作：（查出每个用户的总运费）
1
set
nocount
on
;
2
use
edisondb;
3
declare
@startDT
datetime
4
set
@startDT
=
getdate
()
5
declare
@CustomerTotalFreight
table
6
(
7
custid numeric(
18
,
0
),
8
totalFreight numeric(
18
,
2
)
9
);
10
declare
11
@currentCustid
as
numeric(
18
,
0
),
12
@prvCutstid
as
numeric(
18
,
0
),
13
@currentFreight
as
numeric(
18
,
2
),
14
@totalFreight
as
numeric(
18
,
2
);
15
declare
customerTotalFreight_cursor
cursor
for
--
--声明游标
16
select
custid,freight
17
from
orders
18
order
by
custid;
19
open
customerTotalFreight_cursor
--
--打开游标
20
--
--循环获取每行记录
21
fetch
next
from
customerTotalFreight_cursor
into
@currentCustid
,
@currentFreight
;
22
select
@prvCutstid
=
@currentCustid
,
@totalFreight
=
0.00
;
23
while
@@fetch_status
=
0
24
begin
25
if
@prvCutstid
<>
@currentCustid
26
begin
27
insert
into
@CustomerTotalFreight
values
(
@prvCutstid
,
@totalFreight
);
28
select
@prvCutstid
=
@currentCustid
,
@totalFreight
=
@currentFreight
;
29
end
30
else
31
begin
32
set
@totalFreight
=
@totalFreight
+
@currentFreight
;
33
end
34
fetch
next
from
customerTotalFreight_cursor
into
@currentCustid
,
@currentFreight
;
35
end
;
36
insert
into
@CustomerTotalFreight
values
(
@prvCutstid
,
@totalFreight
);
37
close
customerTotalFreight_cursor;
--
--关闭游标
38
39
deallocate
customerTotalFreight_cursor;
--
--释放游标
40
41
select
*
from
@CustomerTotalFreight
order
by
custid;
42
43
print
'
耗时：
'
+
replace
(
str
(
datediff
(ms,
@startDT
,
getdate
())),
'
'
,
''
)
+
'
毫秒
'
以上功能如果用SQL查询来实现则十分简洁：
1
use
edisondb;
2
declare
@startDT
datetime
3
set
@startDT
=
getdate
()
4
select
custid,
sum
(freight)
as
totalFreight
5
from
orders
6
group
by
custid;
7
print
'
耗时：
'
+
replace
(
str
(
datediff
(ms,
@startDT
,
getdate
())),
'
'
,
''
)
+
'
毫秒
'
