alter table 的功能 create table test(a varchar2(20),b number(2)) 重名命 alter table test rename to test1 (rename test1 to test2) 增删字段 alter table test2 drop column f 修改字段类型和大小 alter table test2 modify d varchar(40) alter table test2 modify f varchar(40) alter table test2 add c varchar2(30) alter table test2 add (d varchar2(30),e number(4)) alter table test2 rename column e to f 处理约束 alter table test2 add constraint pk_mypri primary key (d,f) 利用下面的语句在删除DEPT表中的PRIMARY KEY约束时,同时将删除其它表中引用这个约束的FOREIGN KEY约束: alter table dept drop primary key cascade 加foreign key约束(多字段/表级) alter table employees add constraint emp_jobs_fk foreign key (job,deptno) references jobs (jobid,deptno) on delete cascade |
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