oracle最新sql回忆性演练1

 drop table example; CREATE TABLE example(     ID Number(4) NOT NULL ,     NAME VARCHAR(25),     constraint example_id primary key(id)  );drop SEQUENCE example_sequence;CREATE SEQUENCE example_sequenceINCREMENT BY 1 -- 每次加几个START WITH 1 -- 从1开始计数NOMAXVALUE -- 不设置最大值NOCYCLE -- 一直累加，不循环NOCACHE -- 不建缓冲区;drop TRIGGER example_triger;CREATE TRIGGER example_triger  BEFORE INSERT ON example  FOR EACH ROW  WHEN (new.id is null) --只有在id为空时，启动该触发器生成id号begin  select example_sequence.nextval into :new.id from dual;end;insert into example(name) values('张三');insert into example(id, name) values(111,'李四');insert into example(name) values('张三1');insert into example(name) values('张三2');insert into example(name) values('张三3');select * from example;drop table xxx;create table xxx as select * from example; --复制一个表的数据和结构，但约束不会被复制select * from xxx;--修改主键--1查主键 SELECT   *   from   user_cons_columns c where c.table_name = 'example'; SELECT   *   from   user_cons_columns c where c.table_name = 'xxx';--2删除主键   alter table  example drop constraint example_id;--3增加新的主键约束     alter table example add constraint example_id primary key(id);--4添加列   alter table example add age number;--5删除列   alter table example drop column age;--6修改列(修改列类型的前提：需删除存在的数据库)   alter table example modify age varchar(2);   alter table example modify id varchar(20);--7添加约束 -- foreign key    alter table example add constraint fk_example_xxx foreign key(pid) references xxx(pid);        insert into example(name,age) values('张三1',1);insert into example(name,age) values('张三2',2);insert into example(name,age) values('张三3',113);insert into xxx(name,pid) values('张三2',21);insert into xxx(name,pid) values('张三3',1111);select * from example;select * from xxx;drop table xxx;create table xxx as select * from example;select * from xxx;--alter table xxx add pid number(10);-----处理复制表约束alter table xxx rename column id to sid;alter table xxx add id number;update   xxx set id=sid;alter table xxx drop column sid;-----处理添加字段并为主键alter table xxx add pid varchar2(20);update xxx set pid=id;alter table xxx add constraint xxx_pid primary key(pid);select * from xxx ;----为example表添加外键alter table xxx add constraint fk_xxx foreign key(id) references example(id);--删除约束alter table xxx drop constraint fk_example_xxx;---------处理已有数据的字段类型修改(前4步操作会使表中的约束丢失)--1重命名字段alter table example rename column id to sid;--2添加id字段alter table example add id varchar2(200);  --3更新数据update example set id = sid;--4删除备份数据的字段alter table example drop column sid;--5新增约束alter table example add constraint exmaple_id primary key(id);-------------------------------------------------------------------alter table example add unique(age);alter table example drop unique(age);--查找表的唯一性约束（包括名称，构成列）select column_name  from user_cons_columns cu, user_constraints au where cu.constraint_name = au.constraint_name   and cu.table_name = 'example';-----视图(  如果权限不足，grant connect,resource,dba to 你的实例)create table bbb as select * from example;CREATE  OR  REPLACE  VIEW  exam_sum_v1(name,age) AS SELECT d.name,d.age FROM bbb d;insert into exam_sum_v1(name,age) values('lisii',1221);insert into exam_sum_v1(name,age) values('lisii',1221);insert into exam_sum_v1(name,age) values('lisii',0000);insert into exam_sum_v1(name,age) values('lisii',111);select * from exam_sum_v1;select * from bbb;alter table bbb drop column id;select * from example;select * from xxx;--USER_TAB_COLS中记录了用户表的列信息SELECT USER_TAB_COLS.TABLE_NAME   as 表名,       USER_TAB_COLS.COLUMN_NAME  as 列名,       USER_TAB_COLS.DATA_TYPE    as 数据类型,       USER_TAB_COLS.DATA_LENGTH  as 长度,       USER_TAB_COLS.NULLABLE     as 是否为空,       USER_TAB_COLS.COLUMN_ID    as 列序号,       user_col_comments.comments as 备注  FROM USER_TAB_COLS inner join user_col_comments    on user_col_comments.TABLE_NAME = USER_TAB_COLS.TABLE_NAME   and user_col_comments.COLUMN_NAME = USER_TAB_COLS.COLUMN_NAME；  --关联到表的所有字段信息select col.column_name,       uc.constraint_type,       case uc.constraint_type         when 'P' then          '√'         else          ''       end "PrimaryKey"  from user_tab_columns col  left join user_cons_columns ucc    on ucc.table_name = col.table_name   and ucc.column_name = col.column_name  left join user_constraints uc    on uc.constraint_name = ucc.constraint_name   and uc.constraint_type = 'P' where col.table_name = 'example';--查询某个表中的外键字段名称、所引用表名、所应用字段名select distinct (col.column_name), r.table_name, r.column_name  from user_constraints con,       user_cons_columns col,       (select t2.table_name, t2.column_name, t1.r_constraint_name          from user_constraints t1, user_cons_columns t2         where t1.r_constraint_name = t2.constraint_name           and t1.table_name = 'example') r where con.constraint_name = col.constraint_name   and con.r_constraint_name = r.r_constraint_name   and con.table_name = 'example';