Systemy keruvannya bazamy danykh: MySQL, OLAP, Null, Firebird, Microsoft SQL Server, Informix, PostgreSQL, OLAP-kub, MariaDB, SQLite (Ukrainian Edition)

Dzherelo: Wikipedia. Storinky: 27. Hlavy: MySQL, OLAP, Null, Firebird, Microsoft SQL Server, Informix, PostgreSQL, OLAP-kub, MariaDB, SQLite, Systema keruvannya bazamy danykh, Drizzle, Relyatsiy̆na alhebra, CDS/ISIS, ACID, ODBC, PhpMyAdmin, Superklyuch, Microsoft Access, Kexi, Relyatsiy̆na SKBD, EnterpriseDB Advanced Server, SQL Server Integration Services, Oracle, CRUD, HSQLDB, Pohlyad, Amazon S3, DB2. Vytyah: Null - spetsialʹna poznachka, yaka vykorystovuyetʹsya v SQL dlya poznachennya toho, shcho znachennya ne isnuye v bazi danykh. Vvedeno vynakhidnykom relyatsiy̆noï modeli danykh Edharom Koddom, SQL Null sluhuye dlya vykonannya vymohy, shcho vsi diy̆sno relyatsiy̆ni systemy keruvannya bazamy danykh (RSKBD) pidtrymuyutʹ predstavlennya «vidsutnʹoï i neprydatnoï informatsiï». Kodd takozh vviv vykorystannya maloï litery hretsʹkoï omeha (ω) yak symvola dlya predstavlennya Null v teoriï baz danykh. NULL takozh ye zarezervovanym slovom v SQL, yake vkazuye na spetsialʹnu poznachku Null. Null buv prychynoyu superechok i debativ cherez svoyu asotsiatsiyu z triy̆kovoyu lohikoyu, osoblyvykh vymoh z y̆oho vykorystannya v instruktsiï SQL JOIN, i spetsialʹnoï obrobky ahrehatnymy funktsiyamy ta operatoramy hrupuvannya SQL. Khocha osoblyvi funktsiï ta predykaty pravylʹno obroblyayutʹ Null, oponenty vidchuvayutʹ, shcho pidtrymka tsiyeï mozhlyvosti vvodytʹ nepotribnu skladnistʹ i superechlyvistʹ v relyatsiy̆nu modelʹ danykh. Null buv vvedenyy̆ Edharom Koddom yak zasib dlya predstavlennya vidsutnikh danykh v relyatsiy̆niy̆ modeli nezalezhno vid typu danykh. Vpodalʹshomu vin opublikuvav svoyu stattyu v dvokh chastynakh v chasopysi ComputerWorld, v tsiy̆ statti vin prezentuvav 12 pravyl za yakymy mozhna vyznachyty chy ye SKBD diy̆sno relyatsiy̆noyu. Kodd takozh vviv tryznachnu lohiku, yaka maye try znachennya istynnosti Istyna (True), Khyba (False) ta Nevidomo (Unknown), yaka duzhe blyzʹka do kontseptsiï Null. Znachennya Nevidomo heneruyetʹsya koly Null porivnyuyetʹsy...