SQL/Oracle 两表关联更新

http://blog.csdn.net/cassaba/article/details/6987040

有TA, TB两表，假设均有三个栏位id, name, remark. 现在需要把TB表的name, remark两个栏位通过id关联，更新到TA表的对应栏位。

建表脚本：

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drop table TA;
create table TA
(
id number not null,
name varchar(10) not null,
remark varchar(10) not null
);

drop table TB;
create table TB
(
id number not null,
name varchar(10) not null,
remark varchar(10) not null
);

truncate table TA;
insert into TA values(1, 'Aname1', 'Aremak1');
insert into TA values(2, 'Aname2', 'Aremak2');
commit;

truncate table TB;
insert into TB values(1, 'Bname1', 'Bremak1');
insert into TB values(3, 'Bname3', 'Bremak3');
commit;

select * from TA;
select * from TB;

SQLServer/Oracle版本的Update写法分别如下：

1. SQLServer

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update TA set name=b.name, remark=b.remark from TA a inner join TB b on a.id = b.id

或者

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update TA set name=b.name, remark=b.remark from TA a, TB b where a.id = b.id

注意不要在被更新表的的栏位前面加别名前缀，否则语法静态检查没问题，实际执行会报错。
Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "a.name" could not be bound.

2. Oracle

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update TA a set(name, remark)=(select b.name, b.remark from TB b where b.id=a.id)
where exists(select 1 from TB b where b.id=a.id)

注意如果不添加后面的exists语句，TA关联不到的行name, remark栏位将被更新为NULL值， 如果name, remark栏位不允许为null，则报错。 这不是我们希望看到的。

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--when name, remark is not null, cause error.
--if allow null, rows in TA not matched will be update to null.
update TA a set(name, remark)=(select b.name, b.remark from TB b where b.id=a.id);

可考虑的替代方法：

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update TA a set name= nvl((select b.name from TB b where b.id=a.id), a.name);
update TA a set remark= nvl((select b.remark from TB b where b.id=a.id), a.remark);

如果TA.id, TB.id是unique index或primary key

可以使用视图更新的语法：

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ALTER TABLE TA ADD CONSTRAINT TA_PK
PRIMARY KEY (
ID
)
ENABLE
VALIDATE
;

ALTER TABLE TB ADD CONSTRAINT TB_PK
PRIMARY KEY (
ID
)
ENABLE
VALIDATE
;

update (select a.name, b.name as newname,
a.remark, b.remark as newremark from TA a, TB b where a.id=b.id)
set name=newname, remark=newremark;

更加详尽的对比分析参考下面的文章ORACLE 多表关联 UPDATE 语句