DB2中怎么设置主键

创建表时指定primary key，如：

create table mytab(id int not null primary key,

name char(10)

)

注意，not null 不可省略，必须与primary key 同时指定！

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创建外键时的选项

创建测试表

drop table studentdrop table classdrop table student_classCreate table student(student_id integer not null student_name varchar( ) CONSTRAINT P_KEY_ primary key (student_id)) in luzl_ k_tb index in luzl_ k_tb Create table class(class_id integer not null class_name varchar( ) CONSTRAINT P_KEY_ primary key (class_id)) in luzl_ k_tb index in luzl_ k_tb Create table student_class(student_class_id integer student_id integer class_id integer) in luzl_ k_tb index in luzl_ k_tbalter table student_class add constraint if_class foreign key(class_id) references class(class_id) ON DELETE cascade ON UPDATE RESTRICTalter table student_class add constraint if_student foreign key(student_id) references student(student_id) ON DELETE cascade ON UPDATE RESTRICTInsert into student(student_id student_name) values( luzl )Insert into class(class_id class_name) values( db )Insert into student_class(student_class_id student_id class_id) values( )

On Delete 的选项有

Restrict/no action/cascade/set null 其中cascade选项指定的话 如果删除父记录 依赖于他的子记录也会自动删除 相当于级联删除 如果指定no action和cascade都会报错 因为还有子记录所以无法删除该记录 set nul允许删除父记录并且l会将子表中与父表关联的字段设置为null

On Update 只有两个选项 no action/restrict 它们在更新和删除时并没有区别:如果与子表关联不允许删除

lishixinzhi/Article/program/DB2/201311/21928

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