--8.3 更新資料
use tempdb;
goif object_id('dbo.orderdetails', 'u') is not null drop table dbo.orderdetails
if object_id('dbo.orders', 'u') is not null drop table dbo.orders
select * into dbo.orders from tsqlfundamentals2008.sales.orders;
select * into dbo.orderdetails from tsqlfundamentals2008.sales.orderdetails;
alter table dbo.orders add constraint pk_orders primary key(orderid)
alter table dbo.orderdetails add
constraint pk_orderdetails primary key(orderid, productid),
constraint fk_orderdetails_orders foreign key(orderid) references dbo.orders(orderid);
--8.3.1 update語句
update dbo.orderdetails
set discount = discount + 0.5
where productid = 51
update dbo.orderdetails
set discount += 0.5
where productid = 51
--在sql中所有的賦值表示式好像都是同時進行計算的
--8.3.2 基於聯接的update
update od
set discount += 0.5
from dbo.orderdetails as od
join dbo.orders as o
on od.orderid = o.orderid
where custid = 1;
update dbo.orderdetails
set discount = discount + 0.5
where exists
(select * from dbo.orders
where dbo.orders.orderid = dbo.orderdetails.orderid
and dbo.orders.custid = 1);
--在某些情況下,使用聯接比使用子查詢在效能上更具優勢.除了過濾作用,通過聯接
--還可以訪問其他表的屬性(列)，並在set子句中使用這些屬性為列屬性。
update t1
set t1.col1 = t2.col1,
t1.col2 = t2.col2,
t1.col3 = t2.col3
from dbo.t1 join dbo.t2
on t2.keycol = t1.keycol
where t2.col4='abc'
--8.3.4 賦值update
--tsql支援特殊的update語法,可以在對錶中的資料進行更新的同時為變數賦值
--使用這種特殊的update語法是作為原子操作而進行的，因為它只須要訪問一次資料。
use tempdb;
if object_id('dbo.sequence','u') is not null drop table dbo.sequence;
create table dbo.sequence(val int not null);
insert into dbo.sequence values(10);
declare @nextval as int;
update sequence set @nextval = val = val+1;
select @nextval
--8.4 合併資料
--merge的語句能在一條語句中根據邏輯條件對資料進行不同的修改操作(insert,update和delete).
--用較少的**就可以表達需求，提高查詢效能，因為它可以更少地訪問查詢涉及表。
use tempdb;
if object_id('dbo.customers','u') is not null drop table dbo.customers;
gocreate table dbo.customers
(custid int not null,
companyname varchar(25) not null,
phone varchar(20) not null,
address varchar(50) not null,
constraint pk_customers primary key(custid)
);insert into dbo.customers(custid, companyname, phone, address)
values
(1, 'cust 1', '(111)111-1111', 'address 1'),
(2, 'cust 2', '(222)222-2222', 'address 2'),
(3, 'cust 3', '(333)333-3333', 'address 3'),
(4, 'cust 4', '(444)444-4444', 'address 4'),
(5, 'cust 5', '(555)555-5555', 'address 5');
if object_id('dbo.customersstage', 'u') is not null drop table dbo.customersstage;
gocreate table dbo.customersstage
(custid int not null,
companyname varchar(25) not null,
phone varchar(20) not null,
address varchar(50) not null,
constraint pk_customersstage primary key(custid)
);insert into dbo.customersstage(custid, companyname, phone, address)
values
(2, 'cust 1', '(111)111-1111', 'address 1'),
(3, 'cust 2', '(222)222-2222', 'address 2'),
(5, 'cust 3', '(333)333-3333', 'address 3'),
(6, 'cust 4', '(444)444-4444', 'address 4'),
(7, 'cust 5', '(555)555-5555', 'address 5');
select * from dbo.customers;
select * from dbo.customersstage;
merge into dbo.customers as tgt
using dbo.customersstage as src
on tgt.custid = src.custid
when matched then
update set
tgt.companyname=src.companyname,
tgt.phone=src.phone,
tgt.address=src.address
when not matched then
insert (custid, companyname, phone, address)
values(src.custid, src.companyname, src.phone, src.address);
select * from dbo.customers
第八章 資料修改 1
第8章 資料修改 8.1 插入資料 8.1.1 insert values 語句 use tempdb if object id dbo.orders u is not null drop table dbo.orders create table dbo.orders orderid int no...
第八章 指標 第八章 指標
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