数据库 教程2

//建立表空间,表空间用于存储数据库对象,如表、视图、存储过程等。下面的语句建立一个名为myspace的表空间,数据物理文件为D:\oracle\myspace.dbf,大小为100M //create tablespace myspace datafile 'D:\oracle\myspace.dbf' size 100M; //删除表空间,先执行下面的sql而后删除物理文件 //drop tablespace myspace; //建立用户,用户名为test密码为test。该用户建立的表默认保存在myspace表空间内。多个用户能够共享一个表空间 //create user test identified by test default tablespace myspace temporary tablespace temp; //为用户受权,通常只为用户授予connect,resource角色,由于dba角色权限过高,容易破坏数据库,resource角色权限已经很高。用户的角色权限能够传递 //grant connect,resource,dba to test; /* 建立表和删除表 指定表列名,数据类型,长度限制,列值完整性约束 主键约束保证唯一性和非空性 */ //create table users ( // id integer default 0, //default 约束默认值 // uname varchar2(10) not null unique,  //not null 约束列值不容许为空,unique不容许值重复 // birthday date, // height number(3,2), // folk varchar2(4), // primary key (id) //); //drop table users;  //注意删除表,全部的数据都会丢失 //修改表 //alter table users add (weight number(4,1) ,email varchar2(20));  //增长表列 //alter table users drop column weight;          //删除表列 //alter table users modify (email varchar2(100));       //改变列大小会受列已有数据的限制,如已有数据的类型,长度等 //删除表主键 //alter table users drop primary key; //增长表主键 //alter table users add primary key (id); /* 视图 视图的做用:  视图可以简化用户的操做。  视图机制能够使用户以不一样的方式看待同一数据  视图对数据库的重构提供了必定程度的逻辑独立性  视图能够对机密的数据提供安全保护 建立视图读法: CREATE VIEW <视图名> [(列名1,列名2,......,列名n)] AS <子查询> [WITH CHECK OPTION]； */ //建立视图 //create view v_users as select * from users; //建立有条件选择的视图,用户只能看到身高大于1.75的用户姓名和身高信息 //create view v_users as select uname,height from users where height>1.75; //drop view v_users; /* 基本查询语法 SELECT <目标列组>      FROM <数据源>      [WHERE <元组选择条件> ]      [GROUP BY <分列组> [HAVING  <组选择条件> ]]      [ORDER BY <排序列1>  <排序要求1>  [，…n]]； */ //查询全部记录的全部字段 //select * from users; //查询部分字段 //select id,name,folk from users; //插入数据,注意主键和非空字段必须给定输入值 //不指定列名,输入的值顺序必须和数据库字段顺序(建立表时的顺序)一致；指定的值要和数据库字段一样多 //insert into users values (1,'user1',sysdate,1.75,'汉','[email]user1@email.com[/email]'); commit ; //按指定列的顺序插入数据,而且能够只插入部分数据 //insert into users(id,height,uname,folk) values (2,1.78,'user2','汉'); commit ; //插入测试数据 //insert into users ( ID, UNAME, BIRTHDAY, HEIGHT, FOLK, EMAIL) values (3,'USER3',sysdate,1.74,'鲜','[email]user3@email.com[/email]'); //insert into users ( ID, UNAME, BIRTHDAY, HEIGHT, FOLK, EMAIL) values (4,'user4',current_timestamp,1.76,'鲜','[email]user4@email.com[/email]'); //insert into users ( ID, UNAME, BIRTHDAY, HEIGHT, FOLK, EMAIL) values (5,'USER5',current_date,1.85,'汉','[email]user5@email.com[/email]'); //commit ; // //rollback ; //insert into users (id,uname,height,folk) values (6,'user6',1.73,'鲜'); //insert into users  values (7,'user7',    to_date('1980-01-01','yyyy-mm-dd')    ,1.78,'汉','[email]user7@email.com[/email]'); //insert into users(id,uname,birthday,height) // select id+1 , substr(uname,1,length(uname)-1)||(id+1), sysdate,1.99 from users //   where id = (select max(id) from users); //select * from users where id > 5; //rollback ; //修改数据,注意必定要用where子句限定条件,不然会影响表中全部的记录(如：update users set height = 1.75 全部人的身高都会变为1.75) //update users set height = 1.75,birthday=to_date('1982-08-15','yyyy-mm-dd') where id =1 ; commit ; //删除数据,与update同样要有严格的where子句限制 //delete from users where id = 4; commit ; /* DELETE 不能删除个别的字段,它对于给定表只能删除整条记录 与INSERT 和UPDATE 同样,删除一个表中的记录可能会致使与其它表的引用完整性问题。当对数据库进行修改时必定在头脑中有这个概念。 DELETE 语句只会删除记录不会删除表,若是要删除表需使用DROP TABLE命令 */ //Oracle不能建立自增列,当须要实现基于数据库的自增列须要使用sequence对象,建立sequence简单语句以下： //create sequence seq_pkgen; //查看sequence的当前值 //select seq_pkgen.currval from dual; //使用sequence对象实现列自增 //insert into users(id,uname,folk) values(seq_pkgen.nextVal,user3,'鲜'); commit ; /* select 语句完整语法： [select …] [from …] [where …] [group by …] [having …] [order by…] 除了变量值外,查询语句对大小写并不敏感。 因此 SeLeCT 与 sELEct 以及 SELECT 是相同的。 */ //查询全部数据 //select * from users; //条件查询 //select * from users where id = 5; //选取部分字段 //select id,uname from users; //select users.uname from users; //能够为列和表使用别名,用as关键字 //select uname as username from users as myusers;  //列别名和表别名是能够单独使用的 //或 //select uname username from users; //select myusers.uname username from users myusers; //列别名是username,表别名是myusers,能够用myusers.uname取得uname字段 /* SQL中的运算符 数学运算符+, -, *, / 字符串链接符...||... or concat(...,...) */ //数字和字符常量的计算 //select 1+2,5-6,2*3,6/5,'abc'||'def',concat('abc','def') from dual; //对字段进行运算 //select id+height,id*height from users; //常量与字段混合使用 //select uname||' email : '||email from users; /* 逻辑运算符and, or, not ,[not ]in, any ,all,exists,[not ]between .. and ,is [not] null,[not] like */ //select * from users where uname='a' and height = 20; //select * from users where uname='a' or height = 20; //select * from users where uname='a' and height = 20; //select * from users where uname='a' and height = 20 or uname='b'; //select * from users where exists (select * from users where id >= 5); //select * from users where exists // (select * from user_contact where users.id = 1 and user_contact.address = '北京市海淀区'); //同上 //select * from users ,user_contact where  users.id = 1 and user_contact.address = '北京市海淀区'; //select * from users where id in (1,2); //select * from users where id > any (1,2); //select * from users where id > all (1,2); //select * from users where email is null; //select * from users where email is not null; //查询用户名为user1和user2的用户 //select * from users where uname in ('user1','user2') ; //查询除了user1和user3外的全部用户 //select * from users where uname not in ('user1','user3') ; //查询身高在1.72和1.75之间的记录,包括1.72和1.75 //select * from users where height between 1.72 and 1.77; //等价的语句 //select * from users where height >= 1.72 and height <= 1.77; //查询email是null的记录,注意null与''是不一样的,null表明未知的意义,''是空字符串 //select * from users where email is null; //select * from users where height is not null; //select * from users where email like 'u%'; //select * from users where uname like 'user_'; //经过lower把字段内容变为小写再查询,这样实现不分大小写的查询 //select * from users where lower(email) like 'user%'; //变为大写 //select upper(uname),folk,email from users where upper(email) like 'USER%'; //能够用()对查询条件分组,改变优先级 //select * from users where (uname='user1' and email='[email]user1@email.com[/email]') or email='[email]user3@email.com[/email]'; /* 比较运算符=, >=, <=, <>, !=,^= */ //select * from users where height > 1.76; //select * from users where height >= 1.76; //select * from users where height <> 1.76; //select * from users where height != 1.76; //select * from users where height ^= 1.76; /* 组合查询操做符和其余SQL操做符 语法:  <查询1> <组合操做符> <查询2> union 并集 minus 差查询 intersect 交集 all distinct 抑制重复值 */ //select * from users where id >3 union select * from users where id <5 ; //select * from users where id >1 minus select * from users where id <3 ; //select * from users where id >1 intersect select * from users where id <3 ; //select avg(all height) from users; //通常与统计函数一块儿使用 //select distinct folk from users;   本文转自程式先锋网站 ｗｗｗ.ｊａｖａｂｉｚ.ｃｎ