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