ï»??xml version="1.0" encoding="utf-8" standalone="yes"?>av成人毛片,男女羞羞在线观看,欧美女v视频http://www.aygfsteel.com/stevenjohn/category/52548.html那些青春的岁æœ?/description>zh-cnTue, 04 Sep 2012 17:30:28 GMTTue, 04 Sep 2012 17:30:28 GMT60数据库烦(ch¨³)引约束收é›?/title><link>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387024.html</link><dc:creator>abin</dc:creator><author>abin</author><pubDate>Tue, 04 Sep 2012 15:11:00 GMT</pubDate><guid>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387024.html</guid><wfw:comment>http://www.aygfsteel.com/stevenjohn/comments/387024.html</wfw:comment><comments>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387024.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/stevenjohn/comments/commentRss/387024.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/stevenjohn/services/trackbacks/387024.html</trackback:ping><description><![CDATA[create index aid on abin(id)<br />create unique index usid on abin(sid)<br />//¾l„合索引<br />create unique index allindex on abin(id,name,sid) <br /><a >http://blog.csdn.net/java05/article/details/5579183</a> <br /><br />创徏主键åQ?br />create table abin1(<br />id number(10,0) not null check(id>0),<br />name nvarchar2(100),<br />constraint abin1id primary key(id)<br />);<br /><br />创徏主键和外é”?br />create table abin2(<br />id number(10,0) not null check(id>0),<br />sid number(10,0) not null,<br />name nvarchar2(100),<br />constraint abin2id primary key(id),<br />constraint abin2sid foreign key(sid) references abin1(id)<br />)<br /><br /><img src ="http://www.aygfsteel.com/stevenjohn/aggbug/387024.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/stevenjohn/" target="_blank">abin</a> 2012-09-04 23:11 <a href="http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387024.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>oracle数据库中提供çš?¿Uçº¦æ?/title><link>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387023.html</link><dc:creator>abin</dc:creator><author>abin</author><pubDate>Tue, 04 Sep 2012 15:08:00 GMT</pubDate><guid>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387023.html</guid><wfw:comment>http://www.aygfsteel.com/stevenjohn/comments/387023.html</wfw:comment><comments>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387023.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/stevenjohn/comments/commentRss/387023.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/stevenjohn/services/trackbacks/387023.html</trackback:ping><description><![CDATA[<span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: 14px/21px simsun; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(73,73,73); word-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" class="Apple-style-span">¾U¦æŸä½œç”¨åQšç”¨æ¥ä¿æŒæ•°æ®çš„完整性，防止无效数据˜q›å…¥åˆ°æ•°æ®åº“中ã€?br />oracle数据库中提供çš?¿Uçº¦æ?都是限定某个列或者列的组合的ã€?br />1、主键约æ?PRIMARY KEY)åQ?br />在一个表中能唯一的标识一行。主键可以限定在多个列上ã€?br />3、唯一键约æ?UNIQUE key)åQšåœ¨ä¸€ä¸ªè¡¨ä¸­èƒ½å”¯ä¸€çš„标识一行，唯一键也可以限定在多个列上ã€?br />主键和唯一键的区别åQ?br />a、一个表中最多只能有一个主键。可以多个唯一键ã€?br />b、主键所限定的列不能为null,唯一键所限定的列可以为null.<br />2、外键约æ?FOREIGN key)åQ?br /> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>引用表：(x¨¬)有外键约束的列所在的表ã€?br /> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>被引用表åQšå¤–键所引用的列。被引用的列只能是主键或者唯一键ã€?br />4、非½Iºçº¦æ?NOT null)åQšè¡¨½Cø™¯¥åˆ—上的数据不能有null倹{€?br />5、检查性约æ?check)åQšè¡¨½Cø™¯¥åˆ—上的数据必™åÀL»¡­‘Ïx(ch¨®ng)Ÿä¸€ä¸ªæ¡ä»¶è¡¨è¾‘Ö¼ã€?br /><br />如何创徏¾U¦æŸåQ?br />1、在创徏表的同时创徏¾U¦æŸ<br /> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>a.列çñ”别约束：(x¨¬)在每个列写完之后写约束ã€?br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CREATE TABLE t_08132(id NUMBER(10) PRIMARY KEY ,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>NAME CHAR(10) NOT NULL,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>gender CHAR(2) CHECK (gender IN ('ç”?,'å¥?)),<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>email CHAR(20) UNIQUE<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>)<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08132 VALUES(1,'a','ç”?,'1@neusoft.com') <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08132 VALUES(2,'a','ç”?,'2@neusoft.com') <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08132 VALUES(3,'c','ç”?,'3@neusoft.com') <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08132 VALUES(4,'d','','4@neusoft.com') <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08132 VALUES(5,'e','å¦?,'5@neusoft.com') <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>//外键¾U¦æŸ<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CREATE TABLE t_08133( id NUMBER(10) PRIMARY KEY ,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>NAME CHAR(10) NOT NULL,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>deptno NUMBER(2) REFERENCES dept(deptno) <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>)<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08133 VALUES(1,'a',20) <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>//¾l™çº¦æŸå‘½å?nbsp;<wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CREATE TABLE t_08134(id NUMBER(10) CONSTRAINT t4_id_pk PRIMARY KEY ,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>NAME CHAR(10) CONSTRAINT t4_name_nn NOT NULL,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>gender CHAR(2) CONSTRAINT t4_gen_ck CHECK (gender IN ('ç”?,'å¥?)),<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>email CHAR(20) CONSTRAINT t4_em_uk UNIQUE,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>deptno NUMBER(2) CONSTRAINT t4_deptno_fk REFERENCES dept(deptno) <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>)<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08134 VALUES(5,'e','ç”?,'5@neusoft.com',NULL) <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>INSERT INTO t_08134 VALUES(6,'e','ç”?,'6@neusoft.com',NULL) <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>b.表çñ”别约束：(x¨¬)在所有列写完之后写约束。注意，notnull¾U¦æŸä¸èƒ½å†™åœ¨è¡¨çñ”别上ã€?br /> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CREATE TABLE t_08135(id NUMBER(10) <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>NAME CHAR(10) CONSTRAINT t5_name_nn NOT NULL,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>gender CHAR(2) ,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>email CHAR(20) ,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>deptno NUMBER(2) ,<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CONSTRAINT t5_id_pk PRIMARY KEY (ID),<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CONSTRAINT t5_gen_ck CHECK (gender IN ('ç”?,'å¥?)),<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CONSTRAINT t5_em_uk UNIQUE(email),<br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>CONSTRAINT t5_deptno_fk FOREIGN KEY (deptno) REFERENCES dept(deptno) <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><br /> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>)<br />¾U¦æŸçš„名字：(x¨¬)一般规åˆ?¾U¦æŸæ‰€åœ¨çš„表_¾U¦æŸæ‰€åœ¨çš„列_¾U¦æŸ¾cÕdž‹<br /> <wbr>emp_empno_pk,通常只给主键、外键、唯一键命名ã€?br /><br />2、在创徏表之后创建约æ?br />语法åQ?br />Alter TABLE 表名 ADD [CONSTRAINT ¾U¦æŸå] ¾U¦æŸ¾cÕdž‹ [(列名列表)]<br />CREATE TABLE t08161 (ID NUMBER,NAME CHAR(10),sex CHAR(2) ,email CHAR(10),deptno NUMBER)<br />//在ID字段上添加主键约æ?br />ALTER TABLE t08161 ADD CONSTRAINT t1_id_pk PRIMARY KEY(ID)<br />//在sex字段上添加检查性约æ?br />ALTER TABLE t08161 ADD CONSTRAINT t1_email_ck CHECK (sex IN ('ç”?,'å¥?))<br />//在email上添加唯一性约æ?br />ALTER TABLE t08161 ADD CONSTRAINT t1_email_uk UNIQUE (email)<br />//在deptno上添加外键约æ?引用于deptçš„deptno字段ã€?br />ALTER TABLE t08161 ADD CONSTRAINT t1_deptno_fk FOREIGN KEY (deptno) REFERENCES dept(deptno)<br />//在name上添加非½Iºçº¦æ?br />ALTER TABLE t08161 ADD CONSTRAINT t1_name_nn NOT NULL (NAME) <wbr> <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>//加不ä¸?br /><br />ALTER TABLE t08161 MODIFY NAME NULL <wbr> <wbr><br />ALTER TABLE 表名 MODIFY 字段å?NULL/NOT NULL <wbr> <wbr><span id="wmqeeuq" class="Apple-converted-space"> </span>//通过该语法设¾|®æŸä¸€ä¸ªå­—ŒDµäØ“(f¨´)null或者not NULL.<br />//¾lƒä¹ (f¨¤n)åQ?br />创徏表学生表åQŒé‡Œé¢åŒ…含学åøP¼ˆä¸»é”®åQ‰ï¼Œå§“名åQˆéž½I?,òq´é¾„,入班日期åQ?br />班çñ”¾~–号åQˆå¤–键，引用于dept表部门编åøP¼‰(j¨ª)<br />要求åQŒåœ¨åˆ›å¾å®Œè¡¨ä¹‹åŽå»ºç«‹¾U¦æŸã€?br />CREATE TABLE t08162 (sno NUMBER ,sname CHAR(10) ,sage NUMBER ,indate DATE,classno NUMBER)<br />ALTER TABLE t08162 ADD PRIMARY KEY (sno)<br />ALTER TABLE t08162 MODIFY sNAME NOT NULL<br />ALTER TABLE t08162 ADD FOREIGN KEY(classno) REFERENCES dept(deptno)<br />4、如何删除约æ?br />ALTER TABLE 表名 DROP PRIMARY KEY|UNIQUE (åˆ?|CONSTRAINT ¾U¦æŸå?br />ALTER TABLE t08162 DROP PRIMARY KEY<br />¾lƒä¹ (f¨¤n)åQšåˆ é™¤t08162上的classno上的外键¾U¦æŸ<br />ALTER TABLE t08162 DROP CONSTRAINT sys_c005467<br />5、约束的启用和禁用ã€?br />语法åQ?br />Alter TABLE 表名 Disable|ENABLE CONSTRAINT ¾U¦æŸå?br /><br /></span><img src ="http://www.aygfsteel.com/stevenjohn/aggbug/387023.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/stevenjohn/" target="_blank">abin</a> 2012-09-04 23:08 <a href="http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387023.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>MySql 表的主键索引问题http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387021.htmlabinabinTue, 04 Sep 2012 15:00:00 GMThttp://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387021.htmlhttp://www.aygfsteel.com/stevenjohn/comments/387021.htmlhttp://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387021.html#Feedback0http://www.aygfsteel.com/stevenjohn/comments/commentRss/387021.htmlhttp://www.aygfsteel.com/stevenjohn/services/trackbacks/387021.html2åQŽçƒ¦(ch¨³)引作ç”?/span>

在烦(ch¨³)引列上，除了(ji¨£n)上面提到的有序查找之外，数据库利用各¿Uå„æ ïL(f¨¥ng)š„快速定位技术，能够大大提高查询效率。特别是当数据量非常大，查询涉及(qi¨¢ng)多个表时åQŒä‹É用烦(ch¨³)引往往能ä‹É查询速度加快成千上万倍ã€?/span>

例如åQŒæœ‰3个未索引的表t1ã€?/span>t2ã€?/span>t3åQŒåˆ†åˆ«åªåŒ…含åˆ?/span>c1ã€?/span>c2ã€?/span>c3åQŒæ¯ä¸ªè¡¨åˆ†åˆ«å«æœ‰1000行数据组成，指äØ“(f¨´)1ï½?/span>1000çš„æ•°å€û|¼ŒæŸ¥æ‰¾å¯¹åº”值相½{‰è¡Œçš„查询如下所½Cºã€?/span>

 

SELECT c1,c2,c3 FROM t1,t2,t3 WHERE c1=c2 AND c1=c3

此查询结果应该äØ“(f¨´)1000行，每行包含3个相½{‰çš„倹{€‚在无烦(ch¨³)引的情况下处理此查询åQŒå¿…™åÕd¯»æ‰?/span>3个表所有的¾l„合åQŒä»¥ä¾¿å¾—å‡ÞZ¸ŽWHERE子句盔R…çš„那些行。而可能的¾l„合数目ä¸?/span>1000×1000×1000åQˆåäº¿ï¼‰(j¨ª)åQŒæ˜¾ç„¶æŸ¥è¯¢å°†ä¼?x¨¬)非常慢ã€?/span>

如果å¯ÒŽ(gu¨©)¯ä¸ªè¡¨˜q›è¡Œç´¢å¼•åQŒå°±èƒ½æžå¤§åœ°åŠ é€ŸæŸ¥è¯¢è¿›½E‹ã€‚利用烦(ch¨³)引的查询处理如下ã€?/span>

åQ?/span>1åQ‰ä»Žè¡?/span>t1中选择½W¬ä¸€è¡Œï¼ŒæŸ¥çœ‹æ­¤è¡Œæ‰€åŒ…含的数据ã€?/span>

åQ?/span>2åQ?span>使用è¡?/span>t2上的索引åQŒç›´æŽ¥å®šä½?/span>t2中与t1的值匹配的行。类ä¼û|¼Œåˆ©ç”¨è¡?/span>t3上的索引åQ?/span>直接定位t3中与来自t1的值匹配的行ã€?/span>

åQ?/span>3åQ‰æ‰«æè¡¨t1的下一行åƈ重复前面的过½E‹ï¼Œç›´åˆ°éåŽ†t1中所有的行ã€?/span>

在此情åŞ下，仍然对表t1执行äº?ji¨£n)一个完全扫描，但能够在è¡?/span>t2å’?/span>t3上进行烦(ch¨³)引查扄¡›´æŽ¥å–å‡?gu¨®)™¿™äº›è¡¨ä¸­çš„行，比未用çƒ?ch¨³)引时要快一百万倍ã€?/span>

利用索引åQ?/span>MySQL加速了(ji¨£n)WHERE子句满èƒö条äšg行的搜烦(ch¨³)åQŒè€Œåœ¨å¤šè¡¨˜qžæŽ¥æŸ¥è¯¢æ—Óž¼Œåœ¨æ‰§è¡Œè¿žæŽ¥æ—¶åŠ å¿«äº?ji¨£n)与其他表中的行匚w…çš„速度ã€?/span>

13.4.2 åˆ›å¾ç´¢å¼•

在执è¡?/span>CREATE TABLE语句时可以创建烦(ch¨³)引，也可以单独用CREATE INDEXæˆ?/span>ALTER TABLE来äØ“(f¨´)表增加烦(ch¨³)引ã€?/span>

1åQ?/span>ALTER TABLE

ALTER TABLE用来创徏普通烦(ch¨³)引ã€?/span>UNIQUE索引æˆ?/span>PRIMARY KEY索引ã€?/span>

 

ALTER TABLE table_name ADD INDEX index_name (column_list)

ALTER TABLE table_name ADD UNIQUE (column_list)

ALTER TABLE table_name ADD PRIMARY KEY (column_list)

 

其中table_name是要增加索引的表名，column_list指出对哪些列˜q›è¡Œç´¢å¼•åQŒå¤šåˆ—时各列之间用逗号分隔。烦(ch¨³)引名index_name可选，¾~ºçœæ—Óž¼ŒMySQLž®†æ ¹æ®ç¬¬ä¸€ä¸ªçƒ¦(ch¨³)引列赋一个名¿U°ã€‚另外，ALTER TABLE允许在单个语句中更改多个表，因此可以在同时创建多个烦(ch¨³)引ã€?/span>

2åQ?/span>CREATE INDEX

CREATE INDEX可对表增加普通烦(ch¨³)引或UNIQUE索引ã€?/span>

 

CREATE INDEX index_name ON table_name (column_list)

CREATE UNIQUE INDEX index_name ON table_name (column_list)

 

table_nameã€?/span>index_nameå’?/span>column_listå…ähœ‰ä¸?/span>ALTER TABLE语句中相同的含义åQŒçƒ¦(ch¨³)引名不可选。另外，不能ç”?/span>CREATE INDEX语句创徏PRIMARY KEY索引ã€?/span>

3åQŽçƒ¦(ch¨³)引类åž?/span>

在创建烦(ch¨³)引时åQŒå¯ä»¥è§„定烦(ch¨³)引能否包含重复倹{€‚如果不包含åQŒåˆ™ç´¢å¼•åº”该创徏ä¸?/span>PRIMARY KEYæˆ?/span>UNIQUE索引。对于单列惟一性烦(ch¨³)引，˜q™ä¿è¯å•åˆ—不包含重复的倹{€‚对于多列惟一性烦(ch¨³)引，保证多个值的¾l„合不重复ã€?/span>

PRIMARY KEY索引å’?/span>UNIQUE索引非常¾cÖM¼¼ã€‚事实上åQ?/span>PRIMARY KEY索引仅是一个具有名¿U?/span>PRIMARYçš?/span>UNIQUE索引。这表示一个表只能包含一ä¸?/span>PRIMARY KEYåQŒå› ä¸ÞZ¸€ä¸ªè¡¨ä¸­ä¸å¯èƒ½å…ähœ‰ä¸¤ä¸ªåŒåçš„烦(ch¨³)引ã€?/span>

下面�/span>SQL语句�/span>students表在sid上添�/span>PRIMARY KEY索引�/span>

 

ALTER TABLE students ADD PRIMARY KEY (sid)

 

13.4.3 åˆ é™¤ç´¢å¼•

可利ç”?/span>ALTER TABLEæˆ?/span>DROP INDEX语句来删除烦(ch¨³)引。类ä¼égºŽCREATE INDEX语句åQ?/span>DROP INDEX可以åœ?/span>ALTER TABLE内部作äØ“(f¨´)一条语句处理，语法如下ã€?/span>

 

DROP INDEX index_name ON talbe_name

ALTER TABLE table_name DROP INDEX index_name

ALTER TABLE table_name DROP PRIMARY KEY

 

其中åQŒå‰ä¸¤æ¡è¯­å¥æ˜¯ç­‰ä»ïL(f¨¥ng)š„åQŒåˆ é™¤æŽ‰table_name中的索引index_nameã€?/span>

½W?/span>3条语句只在删é™?/span>PRIMARY KEY索引时ä‹É用，因äØ“(f¨´)一个表只可能有一ä¸?/span>PRIMARY KEY索引åQŒå› æ­¤ä¸éœ€è¦æŒ‡å®šçƒ¦(ch¨³)引名。如果没有创å»?/span>PRIMARY KEY索引åQŒä½†è¡¨å…·æœ‰ä¸€ä¸ªæˆ–多个UNIQUE索引åQŒåˆ™MySQLž®†åˆ é™¤ç¬¬ä¸€ä¸?/span>UNIQUE索引ã€?/span>

如果从表中删除了(ji¨£n)某列åQŒåˆ™ç´¢å¼•ä¼?x¨¬)受到åª?ji¨£ng)响。对于多列组合的索引åQŒå¦‚果删除其中的某列åQŒåˆ™è¯¥åˆ—也会(x¨¬)从烦(ch¨³)引中删除。如果删除组成烦(ch¨³)引的所有列åQŒåˆ™æ•´ä¸ªç´¢å¼•ž®†è¢«åˆ é™¤



]]>数据库主键，唯一é”?/title><link>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387019.html</link><dc:creator>abin</dc:creator><author>abin</author><pubDate>Tue, 04 Sep 2012 14:56:00 GMT</pubDate><guid>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387019.html</guid><wfw:comment>http://www.aygfsteel.com/stevenjohn/comments/387019.html</wfw:comment><comments>http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387019.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/stevenjohn/comments/commentRss/387019.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/stevenjohn/services/trackbacks/387019.html</trackback:ping><description><![CDATA[主键与唯一索引的区别：(x¨¬)<br /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">主键是一¿Uçº¦æŸï¼Œå”¯ä¸€ç´¢å¼•æ˜¯ä¸€¿Uçƒ¦(ch¨³)引，两者在本质上是不同的ã€?/span><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">主键创徏后一定包含一个唯一性烦(ch¨³)引，唯一性烦(ch¨³)引åƈ不一定就是主键ã€?/span><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">唯一性烦(ch¨³)引列允许½Iºå€û|¼Œè€Œä¸»é”®åˆ—不允è®æ€Ø“(f¨´)½Iºå€¹{€?/span><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">主键列在创徏æ—Óž¼Œå·²ç»é»˜è®¤ä¸ºç©ºå€?+ 唯一索引äº?ji¨£n)ã€?/span><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">主键可以被其他表引用为外键，而唯一索引不能ã€?/span><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">一个表最多只能创å»ÞZ¸€ä¸ªä¸»é”®ï¼Œä½†å¯ä»¥åˆ›å»ºå¤šä¸ªå”¯ä¸€ç´¢å¼•ã€?/span><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><br style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; font: small/14px 宋体; white-space: normal; orphans: 2; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px" /><span style="text-align: left; widows: 2; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; display: inline !important; font: small/14px 宋体; white-space: normal; orphans: 2; float: none; letter-spacing: normal; color: rgb(51,51,51); word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">主键更适合那些不容易更改的唯一标识åQŒå¦‚自动递增列、èín份证åïL(f¨¥ng)­‰ã€?/span><br /><br /><br />很简单，主键¾U¦æŸä¸èƒ½é‡å¤åQŒä¸å¯äØ“(f¨´)½Iºï¼ˆNULL)ã€?br />唯一性约束，不能重复åQŒå¯ä¸ºç©º(NULL)åQŒä½†æ˜¯åªèƒ½ç”±ä¸€ä¸ªNULLã€?img src ="http://www.aygfsteel.com/stevenjohn/aggbug/387019.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/stevenjohn/" target="_blank">abin</a> 2012-09-04 22:56 <a href="http://www.aygfsteel.com/stevenjohn/archive/2012/09/04/387019.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item></channel></rss> <footer> <div class="friendship-link"> <a href="http://www.aygfsteel.com/" title="狠狠久久亚洲欧美专区_中文字幕亚洲综合久久202_国产精品亚洲第五区在线_日本免费网站视频">狠狠久久亚洲欧美专区_中文字幕亚洲综合久久202_国产精品亚洲第五区在线_日本免费网站视频</a> </div> </footer> Ö÷Õ¾Ö©Öë³ØÄ£°å£º <a href="http://" target="_blank">Ä«ÓñÏØ</a>| <a href="http://" target="_blank">À´°²ÏØ</a>| <a href="http://" target="_blank">¸§ÖÝÊÐ</a>| <a href="http://" target="_blank">ÓÀÐÞÏØ</a>| <a href="http://" target="_blank">èëµéÊÐ</a>| <a href="http://" target="_blank">×Ô¹±ÊÐ</a>| <a href="http://" target="_blank">ȪÖÝÊÐ</a>| <a href="http://" target="_blank">ÎäÐûÏØ</a>| <a href="http://" target="_blank">ÃÖ¶ÉÏØ</a>| <a href="http://" target="_blank">¼Ò¾Ó</a>| <a href="http://" target="_blank">·ÚÎ÷ÏØ</a>| <a href="http://" target="_blank">°¢°Í¸ÂÆì</a>| <a href="http://" target="_blank">ƽ¹ûÏØ</a>| <a href="http://" target="_blank">¹óÖÝÊ¡</a>| <a href="http://" target="_blank">µÃÈÙÏØ</a>| <a href="http://" target="_blank">º×·åÏØ</a>| <a href="http://" target="_blank">µ¾³ÇÏØ</a>| <a href="http://" target="_blank">Û²³ÇÏØ</a>| <a href="http://" target="_blank">ËÉÔ­ÊÐ</a>| <a href="http://" target="_blank">»³ÈáÇø</a>| <a href="http://" target="_blank">ƽÎäÏØ</a>| <a href="http://" target="_blank">ÐÂÉÛÏØ</a>| <a href="http://" target="_blank">ÒåÎÚÊÐ</a>| <a href="http://" target="_blank">½ð²ýÊÐ</a>| <a href="http://" target="_blank">´ó·½ÏØ</a>| <a href="http://" target="_blank">ËçÖÐÏØ</a>| <a href="http://" target="_blank">Õò¿µÏØ</a>| <a href="http://" target="_blank">ÕØÖÝÏØ</a>| <a href="http://" target="_blank">Î÷²Ø</a>| <a href="http://" target="_blank">ÇàÑôÏØ</a>| <a href="http://" target="_blank">¸ÞÀ¼ÏØ</a>| <a href="http://" target="_blank">ÌúÁëÊÐ</a>| <a href="http://" target="_blank">Ò˳ÇÊÐ</a>| <a href="http://" target="_blank">ÆÁ¶«ÊÐ</a>| <a href="http://" target="_blank">ãôÑôÏØ</a>| <a href="http://" target="_blank">À´·ïÏØ</a>| <a href="http://" target="_blank">ÈÊÊÙÏØ</a>| <a href="http://" target="_blank">³Ç²½</a>| <a href="http://" target="_blank">ÁÙâ¢ÏØ</a>| <a href="http://" target="_blank">¼¯ÏÍÏØ</a>| <a href="http://" target="_blank">¼ªÁÖÊ¡</a>| <script> (function(){ var bp = document.createElement('script'); 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