b'\n_START_ARTICLE_\nDUAL tabula\n_START_PARAGRAPH_\nDUAL tabula ir speci\xc4\x81la vienas rindas tabula, kas pieejama p\xc4\x93c noklus\xc4\x93juma vis\xc4\x81s Oracle datub\xc4\x81z\xc4\x93s. T\xc4\x81 ir noder\xc4\xabga t\xc4\x81du pseidokolonnu datu atlas\xc4\xab\xc5\xa1anai k\xc4\x81 piem\xc4\x93ram - SYSDATE vai USER. Tabulai ir viena kolonna ar datu tipu VARCHAR2(1), nosaukumu DUMMY, kuras v\xc4\x93rt\xc4\xabba ir X.\n_START_SECTION_\nIzmanto\xc5\xa1anas piem\xc4\x93rs\n_START_PARAGRAPH_\nORACE SQL sintaks\xc4\x93 nepiecie\xc5\xa1ams izmantot FROM klauzulu, bet da\xc5\xbeiem vaic\xc4\x81jumiem nav nepiecie\xc5\xa1ams izmanto tabulas - DUAL var tikt viegli izmantots \xc5\xa1\xc4\x81dos gad\xc4\xabjumos._NEWLINE_SELECT 1+1FROM DUAL;SELECT SYSDATEFROM DUAL;SELECT USER _NEWLINE_FROM DUAL;\n_START_SECTION_\nV\xc4\x93sture\n_START_PARAGRAPH_\nDUAL tabulu izveidoja \xc4\x8c\xc4\x81rlzs Veiss (Charles Weiss) no Oracle komp\xc4\x81nijas, tabulu iek\xc5\xa1\xc4\x93jo skatu apvieno\xc5\xa1anas nodro\xc5\xa1in\xc4\x81\xc5\xa1anai:_NEWLINE_Es izveidoju DUAL tabulu k\xc4\x81 pamatobjektu Oracle Datu V\xc4\x81rdn\xc4\xabc\xc4\x81 (Oracle Data Dictionary). To nebija paredz\xc4\x93ts apskat\xc4\xabt atsevi\xc5\xa1\xc4\xb7i, bet izmantot apstr\xc4\x81d\xc4\x81jama skata iek\xc5\xa1ien\xc4\x93. Ideja bija, ka J\xc5\xabs var\xc4\x93tu izpild\xc4\xabt JOIN ar DUAL tabulu un rezult\xc4\x81t\xc4\x81 izveidot divas rindas katrai J\xc5\xabsu tabulas rindai. P\xc4\x93c tam izmantojot GROUP BY rezult\xc4\x81ta apkopojumu, var par\xc4\x81d\xc4\xabt datu apjoma un indeksu apjoma izmantoto atmi\xc5\x86as daudzumu. V\xc4\x81rds "DUAL" \xc5\xa1\xc4\xb7ita piem\xc4\x93rots procesam p\xc4\x81ra veido\xc5\xa1anai no vienas rindas._NEWLINE_S\xc4\x81kotn\xc4\x93ji DUAL tabulai bija divas rindas, bet p\xc4\x93c tam vairs tikai viena rinda.\n_START_SECTION_\nOptimiz\xc4\x81cija\n_START_PARAGRAPH_\nDUAL s\xc4\x81kotn\xc4\x93ji bija tabula un datub\xc4\x81zes dzin\xc4\x93js, kur\xc5\xa1 veica diska oper\xc4\x81cijas, lai atlas\xc4\xabtu datus no DUAL. \xc5\xa0\xc4\xab diska oper\xc4\x81cija parasti bija virtu\xc4\x81la (bez piek\xc4\xbcuves fiziskam diskam), jo diska bloki jau bija sake\xc5\xa1oti atmi\xc5\x86\xc4\x81. L\xc4\xabdz ar to bija liels virtu\xc4\x81lo diskoper\xc4\x81ciju daudzums uz DUAL tabulu._NEWLINE_V\xc4\x93l\xc4\x81kaj\xc4\x81s Oracle datub\xc4\x81zes versijas tika optimiz\xc4\x93tas un datub\xc4\x81ze vairs neveic diskoper\xc4\x81cijas ar DUAL tabulu, kaut ar\xc4\xab paties\xc4\xabb\xc4\x81 DUAL tabula joproj\xc4\x81m eksist\xc4\x93.\n_START_SECTION_\nCit\xc4\x81s datub\xc4\x81\xc5\xbeu sist\xc4\x93m\xc4\x81s\n_START_PARAGRAPH_\nMySQL \xc4\xbcauj izmantot DUAL vaic\xc4\x81jumos kuriem nevajag nek\xc4\x81dus datus no tabul\xc4\x81m.'