Alias (SQL)

An alias is a feature of SQL that is supported by most, if not all, relational database management systems (RDBMSs). Aliases provide users with the ability to reduce the amount of code required for a query, and to make queries simpler to understand. In addition, aliasing is required when doing self joins (i.e. joining a table with itself.)

In SQL, you can alias tables and columns. A table alias is called a correlation name, according to the SQL standard.[1] A programmer can use an alias to temporarily assign another name to a table or column for the duration of the current SELECT query. Assigning an alias does not actually rename the column or table. This is often useful when either tables or their columns have very long or complex names. An alias name could be anything, but usually it is kept short. For example, it might be common to use a table alias such as "pi" for a table named "price_information".

The general syntax of an alias is SELECT * FROM table_name [AS] alias_name. Note that the AS keyword is completely optional and is usually kept for readability purposes. Here is some sample data that the queries below will be referencing:

Department Table
DepartmentID DepartmentName
31 Sales
33 Engineering
34 Clerical
35 Marketing

Using a table alias: 

 SELECT D.DepartmentName FROM Department AS D

We can also write the same query like this (Note that the AS clause is omitted this time): 

 SELECT D.DepartmentName FROM Department D

A column alias is similar: 

 SELECT d.DepartmentId AS Id, d.DepartmentName AS Name FROM Department d

In the returned result sets, the data shown above would be returned, with the only exception being "DepartmentID" would show up as "Id", and "DepartmentName" would show up as "Name".

Also, if only one table is being selected and the query is not using table joins, it is permissible to omit the table name or table alias from the column name in the SELECT statement. Example as follows: 

 SELECT DepartmentId AS Id, DepartmentName AS Name FROM Department d

Some systems, such as Postgres[2] and Presto,[3] support specifying column aliases together with table aliases. E.g. 

 SELECT D.Id FROM Department AS D(Id)

would produce the same result set as before. In this syntax it is permissible to omit aliases for some column names. In the example, an alias was provided for DepartmentId, but omitted for DepartmentName. Columns with unspecified aliases will be left unaliased. This syntax is often used with expressions that do not produce useful table and column names, such as VALUES[4] and UNNEST.[5] As an example, one may conveniently test the above SQL statements without creating an actual Departments table by using expressions such as 

WITH Department(DepartmentId, DepartmentName) AS (VALUES (1, 'HR'), (2, 'IT'))
SELECT DepartmentId AS Id, DepartmentName AS Name FROM Department d;

References

  1. ^ ANSI Standard SQL – Foundation Document – Date: 2010-10-14
  2. ^ PostgreSQL: Documentation: 13: 7.2. Table Expressions
  3. ^ https://prestodb.io/docs/0.248/sql/select.html SELECT — Presto 0.248 Documentation
  4. ^ https://prestodb.io/docs/0.248/sql/values.html#examples VALUES — Presto 0.248 Documentation
  5. ^ https://prestodb.io/docs/0.248/sql/select.html#unnest SELECT — Presto 0.248 Documentation

Read other articles:

Teatre Victòria

Theatre in Barcelona, Spain Teatre VictòriaTeatre Victòria in September 2022Address67 Av. del Paral·lel, Sants-MontjuïcBarcelonaSpainCoordinates41°22′29″N 2°10′08″E / 41.3747756°N 2.1687885°E / 41.3747756; 2.1687885DesignationTheatreWebsiteteatrevictoria.com The Teatre Victòria (Victoria Theatre) is a theatre in Barcelona, Spain. History Origins The theatre's origins begin in 1900, when the two brothers Ricardo and Manuel Soriano inaugurated a wooden p...

 

Saint Thomas (Isole Vergini Americane)

Questa voce sugli argomenti isole degli Stati Uniti d'America e isole dei Caraibi è solo un abbozzo. Contribuisci a migliorarla secondo le convenzioni di Wikipedia. Saint ThomasSaint ThomasGeografia fisicaLocalizzazioneMar dei Caraibi Coordinate18°20′N 64°55′W / 18.333333°N 64.916667°W18.333333; -64.916667Coordinate: 18°20′N 64°55′W / 18.333333°N 64.916667°W18.333333; -64.916667 ArcipelagoIsole Vergini Americane Superficie80,91 km² Geogr...

 

Синелобый амазон

Синелобый амазон Научная классификация Домен:ЭукариотыЦарство:ЖивотныеПодцарство:ЭуметазоиБез ранга:Двусторонне-симметричныеБез ранга:ВторичноротыеТип:ХордовыеПодтип:ПозвоночныеИнфратип:ЧелюстноротыеНадкласс:ЧетвероногиеКлада:АмниотыКлада:ЗавропсидыКласс:Пт�...

Germany in the Eurovision Song Contest 2014

Eurovision Song Contest 2014Country GermanyNational selectionSelection processUnser Song für DänemarkSelection date(s)13 March 2014Selected entrantElaizaSelected songIs It RightSelected songwriter(s)Elżbieta SteinmetzFrank KretschmerAdam KesselhautFinals performanceFinal result18th, 39 pointsGermany in the Eurovision Song Contest ◄2013 • 2014 • 2015► Germany participated in the Eurovision Song Contest 2014 with the song Is It Right, written by El...

 

Apple A13

System on a chip (SoC) designed by Apple Inc. Apple A13 BionicGeneral informationLaunchedSeptember 10, 2019Designed byApple Inc.Common manufacturer(s)TSMCMax. CPU clock rateto 2.65 GHz CacheL2 cache8 MB (performance cores)4 MB (efficient cores)Last level cache16 MB (system cache)Architecture and classificationApplicationMobileTechnology node7 nm (N7P)MicroarchitectureLightning and ThunderInstruction setA64 ARMv8.4-A[1]Physical specificationsTransistors8.5 billionCo...

 

Aleksandr Iaremchuk

Russian Paralympic biathlete Aleksandr IaremchukIaremchuk in 2021Personal informationNationalityRussianBorn (1995-02-19) 19 February 1995 (age 29)[1]Shangaly, Russia[1]SportSportBiathlonCross-country skiingAthleticsDisability classT46 (athletics)ClubArkhangelsk Regional Adaptive Sports SchoolCoached bySergey KodlozerovAmir GumerovIrina Gromova(all winter sports)Vyacheslav Sadovnikov (athletics) Medal record Para-athletics Representing  RPC Paralympic Games 2020 ...

Diane Abbott

Untuk aktris dan penyanyi Amerika Serikat, lihat Diahnne Abbott. Diane AbbottAbbott pada 2017 Menteri Dalam Negeri BayanganMasa jabatan6 Oktober 2016 – 4 April 2020PemimpinJeremy CorbynPendahuluAndy BurnhamPenggantiNick Thomas-SymondsMenteri Kesehatan BayanganMasa jabatan27 Juni 2016 – 6 Oktober 2016PemimpinJeremy CorbynPendahuluHeidi AlexanderPenggantiJon AshworthMenteri Pembangunan Internasional BayanganMasa jabatan13 September 2015 – 27 Juni 2016PemimpinJer...

 

Hadron

Artikel ini tidak memiliki referensi atau sumber tepercaya sehingga isinya tidak bisa dipastikan. Tolong bantu perbaiki artikel ini dengan menambahkan referensi yang layak. Tulisan tanpa sumber dapat dipertanyakan dan dihapus sewaktu-waktu.Cari sumber: Hadron – berita · surat kabar · buku · cendekiawan · JSTOR Hadron ([ˈhædrɒn] ( simak), dari Yunani: ἁδρός, hadrós, kokoh, tebal) dalam ilmu fisika partikel, adalah sebuah partikel yang...

 

Молдавский язык

Не следует путать с молдавским диалектом — диалектом современного румынского языка. Молдавский язык Самоназвание limba moldovenească, лимба молдовеняскэ Страны Приднестровье (непризнанное государство) Регионы Молдавская АССР и Молдавская ССР Официальный статус Госуда...

Mulford T. Hunter House

Historic house in Michigan, United States United States historic placeMulford T. Hunter HouseU.S. National Register of Historic PlacesU.S. Historic districtContributing property Show map of MichiganShow map of the United StatesLocation77 West Hancock StreetDetroit, MichiganCoordinates42°21′19″N 83°3′53″W / 42.35528°N 83.06472°W / 42.35528; -83.06472Built1894ArchitectDonaldson & MeierArchitectural styleQueen AnnePart ofWarren-Prentis Historic Distri...

 

Janaki Medical College

Medical school in Janakpur, Nepal Janaki Medical Collegeजानकी मेडिकल कलेजJanaki medical college premisesMottoTo help enhance the quality of lifeTypePrivateEstablished2003 (2003)AccreditationNepal Medical CouncilAcademic affiliationTribhuvan UniversityDirectorOm Prasad PandeyManagementRam Janaki Health FoundationLocationJanakpur, Nepal26°48′56″N 85°57′14″E / 26.8155°N 85.9539°E / 26.8155; 85.9539CampusUrbanWebsitewww.janaki...

 

Battle of Cerro Gordo

1847 battle of the Mexican–American War Battle of Cerro GordoPart of the Mexican–American WarThe Battle of Cerro Gordo by Carl Nebel.DateApril 18, 1847Locationnear Xalapa, Veracruz, Mexico19°25′44″N 96°41′17″W / 19.429°N 96.688°W / 19.429; -96.688Result American victoryBelligerents  United States MexicoCommanders and leaders Winfield Scott Antonio López de Santa AnnaStrength 8,700 - 12,000[1][page needed] 9,000 - 12,000[1&...

Harefield United F.C.

Association football club in England Football clubHarefield UnitedFull nameHarefield United Football ClubNickname(s)The HaresFounded1868; 156 years ago (1868)GroundPreston Park, Harefield UB9 6NECapacity1,200 (150 seated)[1]ChairmanGary SouthManagerWayne CarterLeagueCombined Counties League Premier Division North2023–24Combined Counties League Premier Division North, 13th of 20 Home colours Away colours Harefield United Football Club are an English football club ba...

 

伯努利定律

此條目需要补充更多来源。 (2020年4月24日)请协助補充多方面可靠来源以改善这篇条目，无法查证的内容可能會因為异议提出而被移除。致使用者：请搜索一下条目的标题（来源搜索：伯努利定律 — 网页、新闻、书籍、学术、图像），以检查网络上是否存在该主题的更多可靠来源（判定指引）。 氣體流入文丘里計。減少流體壓力而增加動能，由圖中兩管水的高度差可以看...

 

Театр кіно імені Тараса Шевченка

Театр кіно імені Тараса Шевченка Театр кіно імені Тараса Шевченка.На честь Шевченко Тарас Григорович 48°00′21″ пн. ш. 37°48′14″ сх. д. / 48.00583° пн. ш. 37.80389° сх. д. / 48.00583; 37.80389Країна  УкраїнаРозташування ДонецькСтатус спадщини пам'ятка архітек...

Philipse Manor Hall State Historic Site

Historic house in New York, United States United States historic placePhilipse Manor HallU.S. National Register of Historic PlacesU.S. National Historic LandmarkNew York State Register of Historic Places The Manor houseInteractive map showing Phillipse Manor Hall’s locationLocationYonkersCoordinates40°56′08″N 73°53′59″W / 40.93556°N 73.89972°W / 40.93556; -73.89972Builtc.1682ArchitectFrederick PhilipseNRHP reference No.66000585NYSRHP No.119...

 

Sayyid

Nobility title in the Islamic world For the given name, see Sayyid (name). SayyidسيدIn the Ottoman Empire, the Sayyids had the privilege of wearing a green turbanRegions with significant populationsMuslim worldReligionsIslamLanguagesArabic, Persian, Somali, Urdu, and others[1][2][3][4][5] Part of a series on IslamUsul al-Fiqh Fiqh Ijazah Ijma Ijtihad Ikhtilaf Istihlal Istihsan Istishab Madhhab Madrasah Manhaj Maslaha Qiyas Taqlid Taqwa Urf Ahkam Far...

 

Mar Mediterraneo

Disambiguazione – Mediterraneo rimanda qui. Se stai cercando altri significati, vedi Mediterraneo (disambigua). Questa voce o sezione sull'argomento idrologia non cita le fonti necessarie o quelle presenti sono insufficienti. Commento: varie porzioni di testo sono completamente prive di fonti a supporto Puoi migliorare questa voce aggiungendo citazioni da fonti attendibili secondo le linee guida sull'uso delle fonti. Mar MediterraneoIl bacino del Mar Mediterraneo in una elabor...

Hooping

Activity or dance using a hula hoop Hooping (also called hula hooping or hoop dance) is the manipulation of and artistic movement or dancing with a hoop (or hoops). Hoops can be made of metal, wood, or plastic. Hooping combines technical moves and tricks with freestyle or technical dancing. Hooping can be practiced to or performed with music. In contrast to the classic toy hula hoop, modern hoopers use heavier and larger diameter hoops, and frequently rotate the hoop around parts of the body ...

 

春潮爛漫海棠紅

本條目存在以下問題，請協助改善本條目或在討論頁針對議題發表看法。 此條目没有列出任何参考或来源。 (2012年6月10日)維基百科所有的內容都應該可供查證。请协助補充可靠来源以改善这篇条目。无法查证的內容可能會因為異議提出而被移除。 此條目需要精通或熟悉色情的编者参与及协助编辑。請邀請適合的人士改善本条目。更多的細節與詳情請參见討論頁。 春潮烂漫�...