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Ïðîãðàììèðîâàíèå >> Ïîíÿòèå sql
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COUNT........................................................................................................................................49 ÈÑÏÎËÜÇÎÂÀÍÈÅ DISTINCT....................................................................................................................................................49 ÈÑÏÎËÜÇÎÂÀÍÈÅ COUNT ÑÎ ÑÒÐÎÊÀÌÈ, À ÍÅ ÇÍÀ×ÅÍÈßÌÈ.......................................................................................50 ÂÊËÞ×ÅÍÈÅ ÄÓÁËÈÊÀÒΠ ÀÃÐÅÃÀÒÍÛÅ ÔÓÍÊÖÈÈ........................................................................................................50 ÀÃÐÅÃÀÒÛ ÏÎÑÒÐÎÅÍÍÛÅ ÍÀ ÑÊÀËßÐÍÎÌ ÂÛÐÀÆÅÍÈÈ...............................................................................................51 ÏÐÅÄËÎÆÅÍÈÅ GROUP BY.......................................................................................................................................................51 ÏÐÅÄËÎÆÅÍÈÅ HAVING............................................................................................................................................................53 ÍÅ ÄÅËÀÉÒÅ ÂËÎÆÅÍÍÛÕ ÀÃÐÅÃÀÒÎÂ.................................................................................................................................54 ÐÅÇÞÌÅ........................................................................................................................................................................................55 ÐÀÁÎÒÀ Ñ SQL.............................................................................................................................................................................55 ÔÎÐÌÈÐÎÂÀÍÈÅ ÂÛÂÎÄΠÇÀÏÐÎÑÎÂ.................................................................................56 ÑÒÐÎÊÈ È ÂÛÐÀÆÅÍÈß............................................................................................................................................................57 ÓÏÎÐßÄÎ×ÅÍÈÅ ÂÛÂÎÄÀ ÏÎËÅÉ..........................................................................................................................................59 ÐÅÇÞÌÅ........................................................................................................................................................................................63 ÐÀÁÎÒÀ Ñ SQL.............................................................................................................................................................................63 ÇÀÏÐÀØÈÂÀÍÈÅ ÌÍÎÃÎ×ÈÑËÅÍÛÕ ÒÀÁËÈÖ ÒÀÊ ÆÅ, ÊÀÊ ÎÄÍÎÉ...................................64 ÎÁÚÅÄÈÍÅÍÈÅ ÒÀÁËÈÖ............................................................................................................................................................65 ÈÌÅÍÀ ÒÀÁËÈÖ È ÑÒÎËÁÖÎÂ..................................................................................................................................................65 ÑÎÇÄÀÍÈÅ 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ÑÎÁÎÉ........................................................................................70 ÊÀÊ ÄÅËÀÒÜ ÎÁÚÅÄÈÍÅÍÈÅ ÒÀÁËÈÖÛ Ñ ÑÎÁÎÉ ?............................................................................................................71 ÏÑÅÂÄÎÍÈÌÛ.............................................................................................................................................................................71 ÓÑÒÐÀÍÅÍÈÅ ÈÇÁÛÒÎ×ÍÎÑÒÈ...............................................................................................................................................72 ÏÐÎÂÅÐÊÀ ÎØÈÁÎÊ...................................................................................................................................................................73 ÁÎËÜØÅ ÏÑÅÂÄÎÍÈÌÎÂ..........................................................................................................................................................74 ÅÙÅ ÁÎËÜØÅ ÊÎÌÏËÅÊÑÍÛÕ ÎÁÚÅÄÈÍÅÍÈÉ....................................................................................................................74 ÐÅÇÞÌÅ........................................................................................................................................................................................76 ÐÀÁÎÒÀ Ñ SQL.............................................................................................................................................................................76 ÂÑÒÀÂÊÀ ÎÄÍÎÃÎ ÇÀÏÐÎÑÀ ÂÍÓÒÐÜ ÄÐÓÃÎÃÎ.....................................................................77 ÊÀÊ ÐÀÁÎÒÀÅÒ ÏÎÄÇÀÏÐÎÑ?..................................................................................................................................................78 ÇÍÀ×ÅÍÈß, ÊÎÒÎÐÛÅ ÌÎÃÓÒ ÂÛÄÀÂÀÒÜ ÏÎÄÇÀÏÐÎÑÛ.................................................................................................79 DISTINCT Ñ 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EXISTS?.............................................................................................................................................................96 ÂÛ1ÁÎÐÑÒÎËÁÖÎÂÑ ÏÎÌÎÙÜÞ EXISTS.............................................................................................................................97 ÈÑÏÎËÜÇÎÂÀÍÈÅ EXISTS Ñ ÑÎÎÒÍÅÑÅÍÍÛÌÈ ÏÎÄÇÀÏÐÎÑÀÌÈ................................................................................97 ÊÎÌÁÈÍÀÖÈß ÈÇ EXISTS È ÎÁÜÅÄÈÍÅÍÈß.........................................................................................................................98 ÈÑÏÎËÜÇÎÂÀÍÈÅ NOT EXISTS................................................................................................................................................99 EXISTS È ÀÃÐÅÃÀÒÛ...................................................................................................................................................................99 ÁÎËÅÅ ÓÄÀ×ÍÛÉ ÏÐÈÌÅÐ 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(NULL)..........................................................................................112 ÈÑÏÎËÜÇÎÂÀÍÈÅ COUNT ÂÌÅÑÒÎ EXISTS........................................................................................................................113 ÐÅÇÞÌÅ......................................................................................................................................................................................114 ÐÀÁÎÒÀ Ñ SQL...........................................................................................................................................................................114 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÏÐÅÄËÎÆÅÍÈß UNION.............................................................................115 ÎÁÚÅÄÈÍÅÍÈÅ ÌÍÎÃÎ×ÈÑËÅÍÍÛÕ ÇÀÏÐÎÑΠ ÎÄÈÍ...............................................................................................116 ÊÎÃÄÀ ÂÛ ÌÎÆÅÒÅ ÄÅËÀÒÜ ÎÁÚÅÄÈÍÅÍÈÅ ÌÅÆÄÓ 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SQL...........................................................................................................................................................................125 ÂÂÎÄ, ÓÄÀËÅÍÈÅ È ÈÇÌÅÍÅÍÈÅ ÇÍÀ×ÅÍÈÉ ÏÎËÅÉ...........................................................127 ÊÎÌÀÍÄÛ ÌÎÄÈÔÈÊÀÖÈÈ ßÇÛÊÀ DML...............................................................................................................................128 ÂÂÎÄ ÇÍÀ×ÅÍÈÉ.......................................................................................................................................................................128 ÂÑÒÀÂÊÀ ÏÓÑÒÛÕ ÓÊÀÇÀÒÅËÅÉ (NULL)...............................................................................................................................128 ÈÌÅÍÎÂÀÍÈÅ ÑÒÎËÁÖÀ ÄËß ÂÑÒÀÂÊÈ (INSERT).............................................................................................................129 ÂÑÒÀÂÊÀ ÐÅÇÓËÜÒÀÒΠÇÀÏÐÎÑÀ.......................................................................................................................................129 ÈÇÌÅÍÅÍÈÅ ÇÍÀ×ÅÍÈÉ ÏÎËß..............................................................................................................................................131 ÌÎÄÈÔÈÖÈÐÎÂÀÍÈÅ ÒÎËÜÊÎ ÎÏÐÅÄÅËÅÍÍÛÕ ÑÒÐÎÊ.................................................................................................131 ÊÎÌÀÍÄÀ UPDATE ÄËß ÌÍÎÃÈÕ ÑÒÎËÁÖÎÂ.....................................................................................................................131 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÂÛÐÀÆÅÍÈÉ ÄËß ÌÎÄÈÔÈÊÀÖÈÈ.....................................................................................................131 ÌÎÄÈÔÈÖÈÐÎÂÀÍÈÅ ÏÓÑÒÛÕ(NULL) ÇÍÀ×ÅÍÈÉ.............................................................................................................132 ÐÅÇÞÌÅ......................................................................................................................................................................................132 ÐÀÁÎÒÀ Ñ SQL...........................................................................................................................................................................133 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÏÎÄÇÀÏÐÎÑÎÂ Ñ ÊÎÌÀÍÄÀÌÈ ÌÎÄÈÔÈÊÀÖÈÈ.................................134 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÏÎÄÇÀÏÐÎÑÎÂ Ñ INSERT.....................................................................................................................135 ÍÅ ÂÑÒÀÂËßÉÒÅ ÄÓÁËÈÊÀÒÛ ÑÒÐÎÊ..................................................................................................................................136 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÏÎÄÇÀÏÐÎÑÎÂ, ÑÎÇÄÀÍÛÕ ÂÎ ÂÍÅØÍÅÉ ÒÀÁËÈÖÅ ÇÀÏÐÎÑÀ.................................................136 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÏÎÄÇÀÏÐÎÑÎÂ Ñ DELETE....................................................................................................................137 ÈÑÏÎËÜÇÎÂÀÍÈÅ ÏÎÄÇÀÏÐÎÑÎÂ Ñ UPDATE...................................................................................................................139 ÑÒÎËÊÍÎÂÅÍÈÅ Ñ ÎÃÐÀÍÈ×ÅÍÈßÌÈ ÏÎÄÇÀÏÐÎÑΠÊÎÌÀÍÄÛ DML.......................................................................139 ÐÅÇÞÌÅ......................................................................................................................................................................................140 ÐÀÁÎÒÀ Ñ SQL...........................................................................................................................................................................140 ÑÎÇÄÀÍÈÅ ÒÀÁËÈÖ...................................................................................................................141 ÊÎÌÀÍÄÀ ÑÎÇÄÀÍÈß 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