MySQL主鍵約束

1、MySQL主鍵約束主鍵不能為空NULL能重復(fù)！唯一約束不能重復(fù)，但可以為空。1.單主鍵約束ykeymysqclreattaeblueser1(-idnptrimkaer,yy-namvearc(2h0)arQuery0OKr,owsa0f.0f1escetcemysqdlescuser1;|Fi|elTdype|Nul|Kley|Defa|id|int|NO|PR|NIULL|nam|vearc(2h0)a|rYE|S|NULL2roiwnse0t(.00由于是主鍵，因此插入的數(shù)據(jù)不能有相同的1(張三f0.f00ecsteecysqilnsienrtu1062230001(李四uplica1r

2、y1.PRIM但非主鍵相同可以:y12張三Qy1000mysqslel*efcrto2mser1;|1|張三|2|張三|2roiwnse0t(00sec)主鍵不能為空，非主鍵可以:mysO1R0482(3000)evra1l(2NeLLL長(zhǎng)三mysevra1l(23,sL)L;Q2ery1OKr,owaf0f00ecsmysser1;1 |張三2 |張三3 |NULL3roiwnse0t(012聯(lián)合主鍵約束myL220d(2h0)a,rQ2ey0a0f0f1eLcetce)d(myL2;e|lTdype|N2l|Kley|Defa|2Elxt|tO|PR|NIULL|me|varc(2h0)a

3、|rNO|PR|NIULL|LL|wvoardc(2h0)a|rYE|S|NULL|3oiwnLe0t(00L添加數(shù)據(jù)，只要主鍵的兩項(xiàng)不全一致就行myL2(張三123Q2ery1OKr,ow0.01myL22張三123Q2ery1OKr,ow0.00myL21李四123f0.f00e44|1|張三|123|1|李四|123|2|張三|1233e0t(00但主鍵不能為空，任何一個(gè)都不行:12)32 李四1048230003自增約束320000f3(2h020.00僅添加非主鍵部分，默認(rèn)從1開(kāi)始:nsienrtuoser3(v1 OrKo,wa0.00ensienrtuoser3(v1 OrKo,

4、wa0.00ensienrtuoser3(v1 OrKo,wa0.00eel*ecrtomuser3|1|2|30t(.003如果對(duì)有定義，可以?xún)H添加一次:33 0003U022011000310013100032022012022022022033roiwnse0t(004建表后添加與刪除主鍵mysqclreattaeblueser4-namvearc(2h0)ar0004(2h020.00添加主鍵：0sa0f.0f2escet0l0icaWtaersn0:|nam|vearc(2h02 roiwnse0t(.00刪除主鍵：y0OrKo,wsa0f.0f2escetr0dsD:upl0ica

5、Wtaersn0:|nam|vearc(2h0)a|rYE|S|NUL2 roiwnse0t(.00sec)添加和刪除聯(lián)合主鍵一樣的道理:y0OrKo,wsa0f.0f1escetr0dsD:upl0icaWtaersn0:|nam|vearc(2h0)a|rNO|PR|NIU2 roiwnse0t(.00sec)Query0OrKo,wsa0f.0f2escetRecor0dsD:upl0icaWtaersn0:|nam|vearc(2h02roiwnse0t(.00修改主鍵約束，和添加主鍵差不多，一般不用這種方法:Query0OrKoRecor0dsD:,wsa0f.0f1escetce)

6、d(upl0icaWtaersn0:ings:|nam|vearc(2h0)a|rNO|NULL|2roiwnse0t(.00sec)唯一約束約束修飾的字段的值不可以重復(fù)可以為空建表后添加amvearc(2h0)ary0OrKo,wsa0f.0f1escety0OrKo,wsa0f.0f1er0dsD:upl0icaWtaersn0(2h02roiwnse0t(.00sec)添加數(shù)據(jù)唯一約束下的字段不能重復(fù)：110001106223000mysqilnsienrt1osevra5l(11,esl：i;siQ1ery1OrKo,waf0f00ecsteecd：(mysqilnsienrt1ose

7、vra5l(11,esNU：L;LQ1ery1OrKo,waf0f00ecsteecd：(|1|zhan|gsan|1|li|si|1|NULL|3 roiwnse0t(00sec：建5表時(shí)2添加mysqclreattaebl1eser6(-namvearc(2h0：a,rQ1ery0OrKo,wsa0f0f1escetce：d(mysqdlesc1ser6;|nam|vearc(2h0：a|rYE|SUN|NIULL|2roiwnse0t(00sec：或-namvearc(2h0：a1rniq1eQ1ery0OrKo,wsa0f0f1escetce：d(|nam|vearc(2h0：a|rY

8、E|SUN|NIULL|2roiwnse0t(01sec：添加多個(gè)唯一約束依舊是兩個(gè)不完全一樣就行-namvearc(2h0：a,rQ1ery0OrKo,wsa0f0f1escetce：d(|nam|vearc(2h0：a|rYE|S|NULL|2roiwnse0t(00sec：mysqilnsienrt1osevra8l(11,eszhan：g;sanQ1ery1OrKo,waf0f00ecsteecd：(mysqilnsienrt1osevra8l(12,eszhan：g;sanQ1ery1OrKo,waf0f00ecsteecd：(|1|zhan|g|2|zhan|g3 roiwnse0

9、t(.01刪除唯一約束y0OrKo,wsa0f.0f1escetr0dsD:upl0icaWtaersn0:|nam|vearc(2h02roiwnse0t(.01修改唯一約束qalltearblueser7modviafryc(2h0ry0OrKo,wsa0f.0f1escetce)d(or0dsD:upl0icaWtaersn0:ings:rc(2h00t(.006非空約束mysqclretaatbelueser9-namvearc(2h0)anrontuQuery0OrKo,wsa0f.0f1mysqdlescuser9;|nam|vearc(2h0)a|rNO|NU2roiwnse0t

10、(.00sec)mysqilnsienrtuoserv9a(li(ud1ERRO1R364(HY000):nFaimysqilnsienrtuosevra9l(u1,eQuery1OrKo,waf0.f00ecstmysqilnsienrtuoser9(vnaaQuery1OrKo,waf0.f00ecstmysqslel*efcrtoumser9;|1|zhan|gsan2roiwnse0t(.00sec)默認(rèn)約束當(dāng)我們插入字段值的時(shí)候，如果沒(méi)有傳值，就會(huì)使用默認(rèn)值1er10(ivdaf0.f00ecste,ln(u1a,emszeser10;11011001evra10l(u1,esaf0.f00ecsteehan,1g9|1|zhan|gs10|1|zhan|gs192roiwnse0t(.00s外.鍵約束涉-及-到-兩-個(gè)-表-(主表、副表mvearc(2h0)ar0OrKo,wsa0f.0f1(2h00OrKo,wsa0f.0f1|nam|vearc(2h02roiwnse0t(.00|name|varc(2h0)a|rYE|S|NU3 roiwnse0t(.00sec)(班1000u班Query1OrKo,waf0f00ecsteecu班1000u班Query1OrKo,waf0f00ecsteec班1