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[o]" accesskey="o" class=""><span>Skrá inn</span></a> </li> </ul> </div> </div> </div> <div id="vector-user-links-dropdown" class="vector-dropdown vector-user-menu vector-button-flush-right vector-user-menu-logged-out" title="Frekari valkostir" > <input type="checkbox" id="vector-user-links-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-user-links-dropdown" class="vector-dropdown-checkbox " aria-label="Persónuleg verkfæri" > <label id="vector-user-links-dropdown-label" for="vector-user-links-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-ellipsis mw-ui-icon-wikimedia-ellipsis"></span> <span class="vector-dropdown-label-text">Persónuleg verkfæri</span> </label> <div class="vector-dropdown-content"> <div id="p-personal" class="vector-menu mw-portlet mw-portlet-personal user-links-collapsible-item" title="Notandavalmynd" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport" class="user-links-collapsible-item mw-list-item"><a href="//donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_is.wikipedia.org&uselang=is"><span>Fjárframlög</span></a></li><li id="pt-createaccount" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Kerfiss%C3%AD%C3%B0a:B%C3%BAa_til_a%C3%B0gang&returnto=SQL" title="Þú ert hvattur/hvött til að búa til aðgang og skrá þig inn; en það er ekki skylda"><span class="vector-icon mw-ui-icon-userAdd mw-ui-icon-wikimedia-userAdd"></span> <span>Búa til aðgang</span></a></li><li id="pt-login" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Kerfiss%C3%AD%C3%B0a:Innskr%C3%A1&returnto=SQL" title="Þú ert hvattur/hvött til að innskrá þig, það er hinsvegar ekki skylda. [o]" accesskey="o"><span class="vector-icon mw-ui-icon-logIn mw-ui-icon-wikimedia-logIn"></span> <span>Skrá inn</span></a></li> </ul> </div> </div> <div id="p-user-menu-anon-editor" class="vector-menu mw-portlet mw-portlet-user-menu-anon-editor" > <div class="vector-menu-heading"> Síður fyrir útskráða notendur <a href="/wiki/Hj%C3%A1lp:Introduction" aria-label="Læra meira um breytingar"><span>Læra meira</span></a> </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-anoncontribs" class="mw-list-item"><a href="/wiki/Kerfiss%C3%AD%C3%B0a:Framl%C3%B6g_m%C3%ADn" title="Listi yfir breytingar frá þessu IP-staðfangi [y]" accesskey="y"><span>Framlög</span></a></li><li id="pt-anontalk" class="mw-list-item"><a href="/wiki/Kerfiss%C3%AD%C3%B0a:Spjallas%C3%AD%C3%B0a_m%C3%ADn" title="Spjall um breytingar frá þessu IP-staðfangi [n]" accesskey="n"><span>Spjall</span></a></li> </ul> </div> </div> </div> </div> </nav> </div> </header> </div> <div class="mw-page-container"> <div class="mw-page-container-inner"> <div class="vector-sitenotice-container"> <div id="siteNotice"></div> </div> <div class="vector-column-start"> <div class="vector-main-menu-container"> <div id="mw-navigation"> <nav id="mw-panel" class="vector-main-menu-landmark" aria-label="Vefsíða"> <div id="vector-main-menu-pinned-container" class="vector-pinned-container"> </div> </nav> </div> </div> <div class="vector-sticky-pinned-container"> <nav id="mw-panel-toc" aria-label="Efni" data-event-name="ui.sidebar-toc" class="mw-table-of-contents-container vector-toc-landmark"> <div id="vector-toc-pinned-container" class="vector-pinned-container"> <div id="vector-toc" class="vector-toc vector-pinnable-element"> <div class="vector-pinnable-header vector-toc-pinnable-header vector-pinnable-header-pinned" data-feature-name="toc-pinned" data-pinnable-element-id="vector-toc" > <h2 class="vector-pinnable-header-label">Efni</h2> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-toc.pin">færa í hliðarstiku</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">fela</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">Byrjun</div> </a> </li> <li id="toc-Dæmi" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Dæmi"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>Dæmi</span> </div> </a> <ul id="toc-Dæmi-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Valkostir" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Valkostir"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Valkostir</span> </div> </a> <ul id="toc-Valkostir-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Tengill" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Tengill"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Tengill</span> </div> </a> <ul id="toc-Tengill-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Efni" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Sýna/fela efnisyfirlit" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Sýna/fela efnisyfirlit</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">SQL</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Fara á grein á öðru tungumáli. Til staðar á 85 tungumálum" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-85" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">85 tungumál</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-als mw-list-item"><a href="https://als.wikipedia.org/wiki/SQL" title="SQL – svissnesk þýska" lang="gsw" hreflang="gsw" data-title="SQL" data-language-autonym="Alemannisch" data-language-local-name="svissnesk þýska" class="interlanguage-link-target"><span>Alemannisch</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D9%84%D8%BA%D8%A9_%D8%A7%D9%84%D8%A7%D8%B3%D8%AA%D8%B9%D9%84%D8%A7%D9%85%D8%A7%D8%AA_%D8%A7%D9%84%D9%85%D9%87%D9%8A%D9%83%D9%84%D8%A9" title="لغة الاستعلامات المهيكلة – arabíska" lang="ar" hreflang="ar" data-title="لغة الاستعلامات المهيكلة" data-language-autonym="العربية" data-language-local-name="arabíska" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/SQL" title="SQL – astúríska" lang="ast" hreflang="ast" data-title="SQL" data-language-autonym="Asturianu" data-language-local-name="astúríska" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/SQL" title="SQL – aserska" lang="az" hreflang="az" data-title="SQL" data-language-autonym="Azərbaycanca" data-language-local-name="aserska" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bar mw-list-item"><a href="https://bar.wikipedia.org/wiki/SQL" title="SQL – Bavarian" lang="bar" hreflang="bar" data-title="SQL" data-language-autonym="Boarisch" data-language-local-name="Bavarian" class="interlanguage-link-target"><span>Boarisch</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/SQL" title="SQL – hvítrússneska" lang="be" hreflang="be" data-title="SQL" data-language-autonym="Беларуская" data-language-local-name="hvítrússneska" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-be-x-old mw-list-item"><a href="https://be-tarask.wikipedia.org/wiki/SQL" title="SQL – Belarusian (Taraškievica orthography)" lang="be-tarask" hreflang="be-tarask" data-title="SQL" data-language-autonym="Беларуская (тарашкевіца)" data-language-local-name="Belarusian (Taraškievica orthography)" class="interlanguage-link-target"><span>Беларуская (тарашкевіца)</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/SQL" title="SQL – búlgarska" lang="bg" hreflang="bg" data-title="SQL" data-language-autonym="Български" data-language-local-name="búlgarska" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%8F%E0%A6%B8%E0%A6%95%E0%A6%BF%E0%A6%89%E0%A6%8F%E0%A6%B2" title="এসকিউএল – bengalska" lang="bn" hreflang="bn" data-title="এসকিউএল" data-language-autonym="বাংলা" data-language-local-name="bengalska" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-br mw-list-item"><a href="https://br.wikipedia.org/wiki/SQL" title="SQL – bretónska" lang="br" hreflang="br" data-title="SQL" data-language-autonym="Brezhoneg" data-language-local-name="bretónska" class="interlanguage-link-target"><span>Brezhoneg</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/SQL" title="SQL – bosníska" lang="bs" hreflang="bs" data-title="SQL" data-language-autonym="Bosanski" data-language-local-name="bosníska" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – katalónska" lang="ca" hreflang="ca" data-title="Structured Query Language" data-language-autonym="Català" data-language-local-name="katalónska" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cdo mw-list-item"><a href="https://cdo.wikipedia.org/wiki/SQL" title="SQL – Mindong" lang="cdo" hreflang="cdo" data-title="SQL" data-language-autonym="閩東語 / Mìng-dĕ̤ng-ngṳ̄" data-language-local-name="Mindong" class="interlanguage-link-target"><span>閩東語 / Mìng-dĕ̤ng-ngṳ̄</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/SQL" title="SQL – tékkneska" lang="cs" hreflang="cs" data-title="SQL" data-language-autonym="Čeština" data-language-local-name="tékkneska" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/SQL" title="SQL – velska" lang="cy" hreflang="cy" data-title="SQL" data-language-autonym="Cymraeg" data-language-local-name="velska" class="interlanguage-link-target"><span>Cymraeg</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – danska" lang="da" hreflang="da" data-title="Structured Query Language" data-language-autonym="Dansk" data-language-local-name="danska" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/SQL" title="SQL – þýska" lang="de" hreflang="de" data-title="SQL" data-language-autonym="Deutsch" data-language-local-name="þýska" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/SQL" title="SQL – gríska" lang="el" hreflang="el" data-title="SQL" data-language-autonym="Ελληνικά" data-language-local-name="gríska" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-en mw-list-item"><a href="https://en.wikipedia.org/wiki/SQL" title="SQL – enska" lang="en" hreflang="en" data-title="SQL" data-language-autonym="English" data-language-local-name="enska" class="interlanguage-link-target"><span>English</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/SQL" title="SQL – esperantó" lang="eo" hreflang="eo" data-title="SQL" data-language-autonym="Esperanto" data-language-local-name="esperantó" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/SQL" title="SQL – spænska" lang="es" hreflang="es" data-title="SQL" data-language-autonym="Español" data-language-local-name="spænska" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Struktuurp%C3%A4ringukeel" title="Struktuurpäringukeel – eistneska" lang="et" hreflang="et" data-title="Struktuurpäringukeel" data-language-autonym="Eesti" data-language-local-name="eistneska" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/SQL" title="SQL – baskneska" lang="eu" hreflang="eu" data-title="SQL" data-language-autonym="Euskara" data-language-local-name="baskneska" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A7%D8%B3%E2%80%8C%DA%A9%DB%8C%D9%88%D8%A7%D9%84" title="اس‌کیوال – persneska" lang="fa" hreflang="fa" data-title="اس‌کیوال" data-language-autonym="فارسی" data-language-local-name="persneska" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/SQL" title="SQL – finnska" lang="fi" hreflang="fi" data-title="SQL" data-language-autonym="Suomi" data-language-local-name="finnska" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – franska" lang="fr" hreflang="fr" data-title="Structured Query Language" data-language-autonym="Français" data-language-local-name="franska" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/Teanga_Strucht%C3%BArtha_Iarratas" title="Teanga Struchtúrtha Iarratas – írska" lang="ga" hreflang="ga" data-title="Teanga Struchtúrtha Iarratas" data-language-autonym="Gaeilge" data-language-local-name="írska" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/SQL" title="SQL – galisíska" lang="gl" hreflang="gl" data-title="SQL" data-language-autonym="Galego" data-language-local-name="galisíska" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-hak mw-list-item"><a href="https://hak.wikipedia.org/wiki/SQL" title="SQL – Hakka Chinese" lang="hak" hreflang="hak" data-title="SQL" data-language-autonym="客家語 / Hak-kâ-ngî" data-language-local-name="Hakka Chinese" class="interlanguage-link-target"><span>客家語 / Hak-kâ-ngî</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/SQL" title="SQL – hebreska" lang="he" hreflang="he" data-title="SQL" data-language-autonym="עברית" data-language-local-name="hebreska" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%8D%E0%A4%B8%E0%A4%95%E0%A5%8D%E0%A4%AF%E0%A5%82%E0%A4%8D%E0%A4%B2" title="ऍसक्यूऍल – hindí" lang="hi" hreflang="hi" data-title="ऍसक्यूऍल" data-language-autonym="हिन्दी" data-language-local-name="hindí" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/SQL" title="SQL – króatíska" lang="hr" hreflang="hr" data-title="SQL" data-language-autonym="Hrvatski" data-language-local-name="króatíska" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/SQL" title="SQL – ungverska" lang="hu" hreflang="hu" data-title="SQL" data-language-autonym="Magyar" data-language-local-name="ungverska" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/SQL" title="SQL – armenska" lang="hy" hreflang="hy" data-title="SQL" data-language-autonym="Հայերեն" data-language-local-name="armenska" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-ia mw-list-item"><a href="https://ia.wikipedia.org/wiki/SQL" title="SQL – interlingua" lang="ia" hreflang="ia" data-title="SQL" data-language-autonym="Interlingua" data-language-local-name="interlingua" class="interlanguage-link-target"><span>Interlingua</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/SQL" title="SQL – indónesíska" lang="id" hreflang="id" data-title="SQL" data-language-autonym="Bahasa Indonesia" data-language-local-name="indónesíska" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – ítalska" lang="it" hreflang="it" data-title="Structured Query Language" data-language-autonym="Italiano" data-language-local-name="ítalska" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/SQL" title="SQL – japanska" lang="ja" hreflang="ja" data-title="SQL" data-language-autonym="日本語" data-language-local-name="japanska" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/SQL" title="SQL – georgíska" lang="ka" hreflang="ka" data-title="SQL" data-language-autonym="ქართული" data-language-local-name="georgíska" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/SQL" title="SQL – kasakska" lang="kk" hreflang="kk" data-title="SQL" data-language-autonym="Қазақша" data-language-local-name="kasakska" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/SQL" title="SQL – kóreska" lang="ko" hreflang="ko" data-title="SQL" data-language-autonym="한국어" data-language-local-name="kóreska" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-ku mw-list-item"><a href="https://ku.wikipedia.org/wiki/SQL" title="SQL – kúrdíska" lang="ku" hreflang="ku" data-title="SQL" data-language-autonym="Kurdî" data-language-local-name="kúrdíska" class="interlanguage-link-target"><span>Kurdî</span></a></li><li class="interlanguage-link interwiki-ky mw-list-item"><a href="https://ky.wikipedia.org/wiki/SQL" title="SQL – kirgiska" lang="ky" hreflang="ky" data-title="SQL" data-language-autonym="Кыргызча" data-language-local-name="kirgiska" class="interlanguage-link-target"><span>Кыргызча</span></a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/SQL" title="SQL – latína" lang="la" hreflang="la" data-title="SQL" data-language-autonym="Latina" data-language-local-name="latína" class="interlanguage-link-target"><span>Latina</span></a></li><li class="interlanguage-link interwiki-lmo mw-list-item"><a href="https://lmo.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – Lombard" lang="lmo" hreflang="lmo" data-title="Structured Query Language" data-language-autonym="Lombard" data-language-local-name="Lombard" class="interlanguage-link-target"><span>Lombard</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/SQL" title="SQL – litháíska" lang="lt" hreflang="lt" data-title="SQL" data-language-autonym="Lietuvių" data-language-local-name="litháíska" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/SQL" title="SQL – lettneska" lang="lv" hreflang="lv" data-title="SQL" data-language-autonym="Latviešu" data-language-local-name="lettneska" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-mhr mw-list-item"><a href="https://mhr.wikipedia.org/wiki/SQL" title="SQL – Eastern Mari" lang="mhr" hreflang="mhr" data-title="SQL" data-language-autonym="Олык марий" data-language-local-name="Eastern Mari" class="interlanguage-link-target"><span>Олык марий</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/SQL" title="SQL – makedónska" lang="mk" hreflang="mk" data-title="SQL" data-language-autonym="Македонски" data-language-local-name="makedónska" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%8E%E0%B4%B8%E0%B5%8D.%E0%B4%95%E0%B5%8D%E0%B4%AF%E0%B5%81.%E0%B4%8E%E0%B5%BD." title="എസ്.ക്യു.എൽ. – malajalam" lang="ml" hreflang="ml" data-title="എസ്.ക്യു.എൽ." data-language-autonym="മലയാളം" data-language-local-name="malajalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/SQL" title="SQL – malaíska" lang="ms" hreflang="ms" data-title="SQL" data-language-autonym="Bahasa Melayu" data-language-local-name="malaíska" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-my mw-list-item"><a href="https://my.wikipedia.org/wiki/SQL" title="SQL – búrmneska" lang="my" hreflang="my" data-title="SQL" data-language-autonym="မြန်မာဘာသာ" data-language-local-name="búrmneska" class="interlanguage-link-target"><span>မြန်မာဘာသာ</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/SQL" title="SQL – hollenska" lang="nl" hreflang="nl" data-title="SQL" data-language-autonym="Nederlands" data-language-local-name="hollenska" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/SQL" title="SQL – nýnorska" lang="nn" hreflang="nn" data-title="SQL" data-language-autonym="Norsk nynorsk" data-language-local-name="nýnorska" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – norskt bókmál" lang="nb" hreflang="nb" data-title="Structured Query Language" data-language-autonym="Norsk bokmål" data-language-local-name="norskt bókmál" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%90%E0%A9%B1%E0%A8%B8.%E0%A8%95%E0%A8%BF%E0%A8%8A.%E0%A8%90%E0%A9%B1%E0%A8%B2" title="ਐੱਸ.ਕਿਊ.ਐੱਲ – púnjabí" lang="pa" hreflang="pa" data-title="ਐੱਸ.ਕਿਊ.ਐੱਲ" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="púnjabí" class="interlanguage-link-target"><span>ਪੰਜਾਬੀ</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/SQL" title="SQL – pólska" lang="pl" hreflang="pl" data-title="SQL" data-language-autonym="Polski" data-language-local-name="pólska" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pnb mw-list-item"><a href="https://pnb.wikipedia.org/wiki/%D8%A7%DB%8C%D8%B3_%DA%A9%DB%8C%D9%88_%D8%A7%DB%8C%D9%84" title="ایس کیو ایل – Western Punjabi" lang="pnb" hreflang="pnb" data-title="ایس کیو ایل" data-language-autonym="پنجابی" data-language-local-name="Western Punjabi" class="interlanguage-link-target"><span>پنجابی</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/SQL" title="SQL – portúgalska" lang="pt" hreflang="pt" data-title="SQL" data-language-autonym="Português" data-language-local-name="portúgalska" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-qu mw-list-item"><a href="https://qu.wikipedia.org/wiki/SQL" title="SQL – kvesjúa" lang="qu" hreflang="qu" data-title="SQL" data-language-autonym="Runa Simi" data-language-local-name="kvesjúa" class="interlanguage-link-target"><span>Runa Simi</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/SQL" title="SQL – rúmenska" lang="ro" hreflang="ro" data-title="SQL" data-language-autonym="Română" data-language-local-name="rúmenska" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/SQL" title="SQL – rússneska" lang="ru" hreflang="ru" data-title="SQL" data-language-autonym="Русский" data-language-local-name="rússneska" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/SQL" title="SQL – serbókróatíska" lang="sh" hreflang="sh" data-title="SQL" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="serbókróatíska" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – Simple English" lang="en-simple" hreflang="en-simple" data-title="Structured Query Language" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – slóvakíska" lang="sk" hreflang="sk" data-title="Structured Query Language" data-language-autonym="Slovenčina" data-language-local-name="slóvakíska" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/SQL" title="SQL – slóvenska" lang="sl" hreflang="sl" data-title="SQL" data-language-autonym="Slovenščina" data-language-local-name="slóvenska" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/SQL" title="SQL – albanska" lang="sq" hreflang="sq" data-title="SQL" data-language-autonym="Shqip" data-language-local-name="albanska" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/SQL" title="SQL – serbneska" lang="sr" hreflang="sr" data-title="SQL" data-language-autonym="Српски / srpski" data-language-local-name="serbneska" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Structured_Query_Language" title="Structured Query Language – sænska" lang="sv" hreflang="sv" data-title="Structured Query Language" data-language-autonym="Svenska" data-language-local-name="sænska" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%95%E0%AE%9F%E0%AF%8D%E0%AE%9F%E0%AE%AE%E0%AF%88%E0%AE%AA%E0%AF%8D%E0%AE%AA%E0%AF%81%E0%AE%B3%E0%AF%8D%E0%AE%B3_%E0%AE%B5%E0%AE%BF%E0%AE%A9%E0%AE%B5%E0%AF%81_%E0%AE%AE%E0%AF%8A%E0%AE%B4%E0%AE%BF" title="கட்டமைப்புள்ள வினவு மொழி – tamílska" lang="ta" hreflang="ta" data-title="கட்டமைப்புள்ள வினவு மொழி" data-language-autonym="தமிழ்" data-language-local-name="tamílska" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-tet mw-list-item"><a href="https://tet.wikipedia.org/wiki/SQL" title="SQL – tetúm" lang="tet" hreflang="tet" data-title="SQL" data-language-autonym="Tetun" data-language-local-name="tetúm" class="interlanguage-link-target"><span>Tetun</span></a></li><li class="interlanguage-link interwiki-tg mw-list-item"><a href="https://tg.wikipedia.org/wiki/SQL" title="SQL – tadsjikska" lang="tg" hreflang="tg" data-title="SQL" data-language-autonym="Тоҷикӣ" data-language-local-name="tadsjikska" class="interlanguage-link-target"><span>Тоҷикӣ</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%A0%E0%B8%B2%E0%B8%A9%E0%B8%B2%E0%B8%AA%E0%B8%AD%E0%B8%9A%E0%B8%96%E0%B8%B2%E0%B8%A1%E0%B9%80%E0%B8%8A%E0%B8%B4%E0%B8%87%E0%B9%82%E0%B8%84%E0%B8%A3%E0%B8%87%E0%B8%AA%E0%B8%A3%E0%B9%89%E0%B8%B2%E0%B8%87" title="ภาษาสอบถามเชิงโครงสร้าง – taílenska" lang="th" hreflang="th" data-title="ภาษาสอบถามเชิงโครงสร้าง" data-language-autonym="ไทย" data-language-local-name="taílenska" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tl mw-list-item"><a href="https://tl.wikipedia.org/wiki/SQL" title="SQL – tagalog" lang="tl" hreflang="tl" data-title="SQL" data-language-autonym="Tagalog" data-language-local-name="tagalog" class="interlanguage-link-target"><span>Tagalog</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/SQL" title="SQL – tyrkneska" lang="tr" hreflang="tr" data-title="SQL" data-language-autonym="Türkçe" data-language-local-name="tyrkneska" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-tt mw-list-item"><a href="https://tt.wikipedia.org/wiki/SQL" title="SQL – tatarska" lang="tt" hreflang="tt" data-title="SQL" data-language-autonym="Татарча / tatarça" data-language-local-name="tatarska" class="interlanguage-link-target"><span>Татарча / tatarça</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/SQL" title="SQL – úkraínska" lang="uk" hreflang="uk" data-title="SQL" data-language-autonym="Українська" data-language-local-name="úkraínska" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D8%A7%DB%8C%D8%B3_%DA%A9%DB%8C%D9%88_%D8%A7%DB%8C%D9%84" title="ایس کیو ایل – úrdú" lang="ur" hreflang="ur" data-title="ایس کیو ایل" data-language-autonym="اردو" data-language-local-name="úrdú" class="interlanguage-link-target"><span>اردو</span></a></li><li class="interlanguage-link interwiki-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/SQL" title="SQL – úsbekska" lang="uz" hreflang="uz" data-title="SQL" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="úsbekska" class="interlanguage-link-target"><span>Oʻzbekcha / ўзбекча</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/SQL" title="SQL – víetnamska" lang="vi" hreflang="vi" data-title="SQL" data-language-autonym="Tiếng Việt" data-language-local-name="víetnamska" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/SQL" title="SQL – wu-kínverska" lang="wuu" hreflang="wuu" data-title="SQL" data-language-autonym="吴语" data-language-local-name="wu-kínverska" class="interlanguage-link-target"><span>吴语</span></a></li><li class="interlanguage-link interwiki-yo mw-list-item"><a href="https://yo.wikipedia.org/wiki/SQL" title="SQL – jórúba" lang="yo" hreflang="yo" data-title="SQL" data-language-autonym="Yorùbá" data-language-local-name="jórúba" class="interlanguage-link-target"><span>Yorùbá</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/SQL" title="SQL – kínverska" lang="zh" hreflang="zh" data-title="SQL" data-language-autonym="中文" data-language-local-name="kínverska" class="interlanguage-link-target"><span>中文</span></a></li><li class="interlanguage-link interwiki-zh-min-nan mw-list-item"><a href="https://zh-min-nan.wikipedia.org/wiki/SQL" title="SQL – Minnan" lang="nan" hreflang="nan" data-title="SQL" data-language-autonym="閩南語 / Bân-lâm-gú" data-language-local-name="Minnan" class="interlanguage-link-target"><span>閩南語 / Bân-lâm-gú</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/SQL" title="SQL – kantónska" lang="yue" hreflang="yue" data-title="SQL" data-language-autonym="粵語" data-language-local-name="kantónska" class="interlanguage-link-target"><span>粵語</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q47607#sitelinks-wikipedia" title="Breyta tungumálatenglum" class="wbc-editpage">Breyta tenglum</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav 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data-unpinned-container-id="vector-appearance-unpinned-container" > <div class="vector-pinnable-header-label">Útlit</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-appearance.pin">færa í hliðarstiku</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">fela</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">Úr Wikipediu, frjálsa alfræðiritinu</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="is" dir="ltr"><p><b>SQL</b> (<a href="/wiki/Skammst%C3%B6fun" title="Skammstöfun">skammstöfun</a> fyrir „<b>S</b>tructured <b>Q</b>uery <b>L</b>anguage“) er mjög algengt <a href="/w/index.php?title=Fyrirspurnarm%C3%A1l&action=edit&redlink=1" class="new" title="Fyrirspurnarmál (síða er ekki enn til)">fyrirspurnarmál</a> sem notað er til að búa til, vinna með og sækja gögn úr <a href="/wiki/Gagnagrunnur" title="Gagnagrunnur">gagnagrunnum</a>. </p><p>Auk grunn SQL bjóða margir framleiðendur gagnagrunnskerfa sérstök stefjumál mál svo sem <a href="/wiki/Transact-SQL" title="Transact-SQL">Transact-SQL</a> fyrir Microsoft SQL Server, <a href="/wiki/PL/SQL" title="PL/SQL">PL/SQL</a> fyrir Oracle og <a href="/w/index.php?title=PostgreSQL&action=edit&redlink=1" class="new" title="PostgreSQL (síða er ekki enn til)">PostgreSQL</a> hefur mál, <a href="/w/index.php?title=PL/pgSQL&action=edit&redlink=1" class="new" title="PL/pgSQL (síða er ekki enn til)">PL/pgSQL</a>, keimlíkt þeirra. Líka hefur mál, <a href="/w/index.php?title=SQL/PSM&action=edit&redlink=1" class="new" title="SQL/PSM (síða er ekki enn til)">SQL/PSM</a>, verið staðlað. Þessi mál eru stundum notuð til að búa til föll og stefjur sem keyra í grunninum sjálfum. <a href="/w/index.php?title=IBM_Db2&action=edit&redlink=1" class="new" title="IBM Db2 (síða er ekki enn til)">IBM Db2</a> hefur eigið mál, sem er líkt þeim staðli. Sumir grunnar, hafa ekki haft stefjumál um árabil, enda er hægt í flestum tilvikum að komast hjá því að nota, og nota grunn SQL eingöngu. Þetta átti við um MySQL, sem á endanum fékk stefjumál. </p><p>SQL málið er <a href="/w/index.php?title=ANSI&action=edit&redlink=1" class="new" title="ANSI (síða er ekki enn til)">ANSI</a> og <a href="/wiki/ISO" class="mw-redirect" title="ISO">ISO</a> <a href="/w/index.php?title=Sta%C3%B0all&action=edit&redlink=1" class="new" title="Staðall (síða er ekki enn til)">staðlað</a> (fyrst staðlað 1986, svo í mörgum útgáfum: t.d. SQL-92, þá án t.d. stefjumálsins). Framleiðendur gagnagrunnskerfa útfæra SQL oft á mismunandi hátt (flest kerfi uppfylla SQL-92 hið minnsta, en sennilega nær enginn nýjustu staðla fá að fullu upp í SQL:2016), jafnvel sama gamla staðalinn eða hafa hið minnsta ekki tekið inn nýlegar breytingar, og stundum með því að bæta við eiginleikum sem ekki eru tilgreindir í stöðlunum (sem gerir færanleika forrita milli gagnagrunna erfiðan, hið minnsta ef nýlegir fídusar eru notaður sem aðrir hafa ekki enn uppfyllt). </p><p>SQL notast við þrígilda lógik (e. <i>three-valued logic</i> (3VL) <i>(true/false/unknown)</i>) þ.e. ekki "<a href="/wiki/R%C3%B6ka%C3%B0ger%C3%B0" title="Rökaðgerð">Boolean</a>" (ísl. <i>Búlska</i>) lógík (eingöngu), sem notast bara við <i>satt</i> og <i>ósatt</i>. Þriðju möguleikinn, sá "óþekkti", sem er ekki í Boolean lógík, gengur undir nafninu NULL í SQL. Þ.e. hægt er að athuga sem dæmi, ekki aðeins er_í_sambúð = true, eða er_í_sambúð = false (sumir grunnar leyfa t.d. 't' og 'f' í stað true og false), heldur líka er_í_sambúð IS NULL (eða er_í_sambúð IS NOT NULL), og fá þannig fram þá sem ekki er vitað um (eða hefur ekki enn verið skráð um í gagnagrunninn). Í mörgm tilvikum viljum við ekki þurfa að huga að þeim möguleika, sem flækir réttar fyrirspurnir; þá þvingum við fram að ekki sé hægt að skrá NULL (sem sjálfgefið gildi ef ekki talið upp í INSERT skipun, en skilar annars villu með þessum fyrirvara, sem forrit ætti að grípa), til að byrja með, í viðkomandi svæði í grunninum, með því að skilgreina þau sem NOT NULL í CREATE skipun (eða breyta eftirá með ALTER). NOT NULL er sjálfgefið fyrir PRIMARY KEY svæði, svæði sem töflur ættu að hafa skilgreint (annars er réttleiki ekki tryggður). Einnig er hægt að skilgreina önnur einkvæm svæði með UNIQUE skigreiningu. </p><p>Flestir SQL gagnagrunnar eru "strang-tagaðir", ein af fáum undantekningum er <a href="/w/index.php?title=SQLite&action=edit&redlink=1" class="new" title="SQLite (síða er ekki enn til)">SQLite</a>. Hann er líka sérhæfður "embedded" gagnagrunnur (látinn fylgja með öðrum forritum, jafnvel stýrikerfum, sem nota, t.d. macOS í tilfelli SQLite), ekki hugsaður sem "fjölnotenda" (ólíkt flestum SQL grunnum), þ.e. hver grunnur er ekki notaður af mörgum notendum í einu. Hins vegar er eitt eintak keyrandi t.d. í mörgum vöfrum, og þar með t.d. í nær öllum smartsímum, svo samanlagður notendafjöldi er himinhár og SQLite vinsælasti gagnagrunnur í heimi, meira notaður en þessir hefbundu (sem eru t.d. notaðir af bönkum út um allan heim). </p> <div class="mw-heading mw-heading2"><h2 id="Dæmi"><span id="D.C3.A6mi"></span>Dæmi</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=SQL&veaction=edit&section=1" title="Breyti hluta: Dæmi" class="mw-editsection-visualeditor"><span>breyta</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=SQL&action=edit&section=1" title="Edit section's source code: Dæmi"><span>breyta frumkóða</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>SQL skipanir skilgreina ekki hvernig á að framkvænma ákveðnar aðgerðir, heldur hvað eigi að gera. Samkvæmt SQL staðli verða þær að enda á semíkommu (en þó krefjast ekki allir gagnagrunnar að þær fylgi með). </p><p>Dæmi um mjög einfalda SQL skipun er </p> <pre>SELECT nafn, heimili, postnumer FROM vidskiptamenn; </pre> <p>Ofangreind skipun sækir gögn úr töflunni vidskiptamenn. Engar takmarkanir eru setta við því hvaða færslur eru sóttar, þannig að allar færslurnar sem eru í töflunni verða sóttar. Ekki er gerð nein krafa um í hvaða röð færslurnar eiga að koma þannig að þær geta komið í hvaða röð sem er, og röðin getur hæglega breyst frá fyrirspurn til fyrirspurnar. </p><p>Fyrirspurnin: </p> <pre>SELECT nafn, heimili, postnumer FROM vidskiptamenn WHERE postnumer = '101' ORDER BY heimili, nafn; </pre> <p>myndi hins vegar alltaf skila færslum í röð eftir heimili og innan heimilisfangs í nafnaröð. Einnig takmarkar þessi fyrirspurn færslur við þá sem búa í póstnúmeri 101. </p><p>Til þess að útbúa töflur notum við CREATE skipunina: </p> <pre>CREATE TABLE vidskiptamenn (vskm_numer varchar(10) CONSTRAINT pk_vskm PRIMARY KEY, nafn varchar(100) NOT NULL, heimili varchar(100), postnumer char(3) ); </pre> <p>Lykilorð eins og CREATE geta verið hvort heldur sem er í há eða lágstöfum. Hér er búin tafla sem heitir vidskiptamenn og sett á hana þau skilyrði að dálkur sem kallast vskm_numer sé lykill að færslum í töflunni. Einnig er sett það skilyrði að nafn verður alltaf að vera tilgreint. </p><p>Gögn eru sett inn í töflur með INSERT skipunum. Dæmi. </p> <pre>INSERT INTO vidskiptamenn (vskm_numer, nafn, heimili, postnumer) VALUES ('VSK001', 'Nýja Búðin', 'Austurstræti 1', '101'); </pre> <p>Engin skylda er að lykilorðin séu með stórum staf, en margir vilja að þau séu áberandi. Gagnatögin ("gagnatýpurnar") t.d. CHAR or VARCHAR (strangt til tekið ekki lykilorð), er smekksatriði hvort séu líka með stórum en oft haft með litlum líkt of dálkaheitin. Flestir grunnar hafa VARCHAR, alla vega undir öðru nafni, en t.d. nafn hér að ofan geymir þannig ekki alltaf jafn mörg bæti til að spara pláss, á meðan CHAR fyllir upp í aftan á strengi með bilum og eyðir diskplássi. Sumir grunnar, t.d. PostgreSQL, leyfa að skilgreina ný gagnatög; sem dæmi gæti "<a href="/wiki/Kennitala" title="Kennitala">kennitala</a>" verið notað í stað char(10), sem þó er mjög algengt að nota (en aldrei gagnatag fyrir tölur, því þær tína núllum framan af "textastrengjum"). Meira gagnleg ný gagnatög væri POINT (sem geymir x, y eða x, y og z), ekki af því að miklu máli skiptir að geyma hnit sem "object" upp á hraða við t.d. skráningu, eða að sem object tækju gögn minna pláss (gerir það sennilega ekki), heldur í sumum grunnum, eru til dæmis indexar á meira en gögn í einni vídd. Það getur skipt miklu máli við uppflettingu á gögnum í sérhæfðum kerfum, t.d. landupplýsingakerfum. </p> <div class="mw-heading mw-heading2"><h2 id="Valkostir">Valkostir</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=SQL&veaction=edit&section=2" title="Breyti hluta: Valkostir" class="mw-editsection-visualeditor"><span>breyta</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=SQL&action=edit&section=2" title="Edit section's source code: Valkostir"><span>breyta frumkóða</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Valkostir í stað SQL (sem sumir hverjir virka með sömu SQL gagnagrunnunum því þeir "þýða" yfir í SQL), eru t.d. LINQ, Java Persistence Query Language (JPQL), Object Query Language, XQuery og fleiri. Margir staðlanna eru sögulega áhugaveðir mögulega úreldir eða voru gerðir til að leysa SQL af hólmi en hafa ekki enn gert að nokkru ráði: Tutorial D, Datalog, IBM Business System 12 (IBM BS12), QBE (Query By Example) búið til af Moshè Zloof hjá IBM 1977 og Quel (frá 1974; U.C. Berkeley Ingres project). </p><p>Til eru svokallaðir <a href="/wiki/NoSQL" title="NoSQL">NoSQL</a> gagnagrunnar (nýrri en SQL grunnar, en "fræðin" á bak við þá ef svo má kalla, er í einhverjum tilvikum lík "network" grunnum sem SQL/venslagrunnarnir leystu af hólmi), stundum kallaðir <i>not only SQL</i>, því sumir "noSQL" grunnar styðja nú líka SQL. Þetta er flokkur mismunandi gagnagrunna (t.d. "key-value" ein tegund og "graph" önnur), sem upphaflega studdu ekki SQL, og hefðbundið innihalda "unstructured" gögn. Sem flokkur hafnaði þessi tegund grunna SQL og að einhverju eða öllu leiti, venslagrunnsfræðum (og "normaliseringu"), sem óþörfum, eða að þau ættu aðeins vel við fyrir gögn á ákvenu formi ("structured" gögn). Uppbygging þeirra er önnur og notendur/forritarar nálgast þá/hanna á annan hátt. T.d. er fyrirspurnamálið (frá þeirra upphafsdögum) ekki SQL, og niðurstaðan úr fyrirspurn í þá hefbundið ekki "tafla" (sem SQL grunnar skila), en getur verið á nokkrum mismunandi formum eftir tegund þeirra, en oftast er boðið upp á eina tegund niðursöðu sem líklegast á <a href="/w/index.php?title=JSON&action=edit&redlink=1" class="new" title="JSON (síða er ekki enn til)">JSON</a> (eða álíka) formi. Þar sem SQL fyrirspurnamálið hefur sína kosti, er í auknum mæli að framleiðendur bæti þeim möguleika við. Á sama hátt hafa framleiðendur SQL/venslagrunna bætt við "noSQL" möguleika. Annað hvort einhverju með svipað notagildi eða með sömu forritaskilum (og t.d. <a href="/w/index.php?title=MongoDB&action=edit&redlink=1" class="new" title="MongoDB (síða er ekki enn til)">MongoDB</a>, einum af vinsælu noSQL grunnunum, einn af upphaflegu). PostgreSQL hefur t.d. bætti við <a href="/w/index.php?title=JSON&action=edit&redlink=1" class="new" title="JSON (síða er ekki enn til)">JSON</a> gagnatagi (og JSONB, B fyrir "binary", hliðstætt við BSON í MongoDB). </p> <div class="mw-heading mw-heading2"><h2 id="Tengill">Tengill</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=SQL&veaction=edit&section=3" title="Breyti hluta: Tengill" class="mw-editsection-visualeditor"><span>breyta</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=SQL&action=edit&section=3" title="Edit section's source code: Tengill"><span>breyta frumkóða</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://www.mysql.com/">Heimasíða MySQL</a>, frjáls SQL-gagnagrunns (líka til sem MariaDB afbrigði)</li> <li><a rel="nofollow" class="external text" href="https://www.postgresql.org/">Heimasíða PostgreSQL</a>, frjáls SQL-gagnagrunns, sem styður SQL staðla einna best</li></ul>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Sótt frá „<a dir="ltr" href="https://is.wikipedia.org/w/index.php?title=SQL&oldid=1635134">https://is.wikipedia.org/w/index.php?title=SQL&oldid=1635134</a>“</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Kerfiss%C3%AD%C3%B0a:Flokkar" title="Kerfissíða:Flokkar">Flokkar</a>: <ul><li><a href="/w/index.php?title=Flokkur:SQL&action=edit&redlink=1" class="new" title="Flokkur:SQL (síða er ekki enn til)">SQL</a></li><li><a href="/w/index.php?title=Flokkur:Gagnagrunnar&action=edit&redlink=1" class="new" title="Flokkur:Gagnagrunnar (síða er ekki enn til)">Gagnagrunnar</a></li><li><a href="/wiki/Flokkur:Forritunarm%C3%A1l" title="Flokkur:Forritunarmál">Forritunarmál</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> Þessari síðu var síðast breytt 12. maí 2019, klukkan 11:40.</li> <li id="footer-info-copyright">Textinn er gefinn út samkvæmt <a href="/wiki/Wikipedia:H%C3%B6fundar%C3%A9ttur" title="Wikipedia:Höfundaréttur">Creative Commons Tilvísun-DeilaEins leyfi</a>. 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