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1 讌 螻覦 覿襯 #讌 螻覦 一 2螳讌襦 覿襯 危エ覲 . 蠏 2螳讌 螳.
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2 SQL 煙 讌 螻覦 #蠏碁る 讌讌襦 螻殊 讌朱襷 螳覃 SQL 燕 蟾? 手 覲碁. ろ 谿 螻覦 SQL 燕伎 蟆 譬 SQL 襷 . 覓朱 譟郁唄 . 蠏 譟郁唄 DBMS 企 企 螻 伎 る 蟆企. 一蟇 DBMS 谿 語企 焔螻, 谿 語企 豌襴蠍 覓語企. (轟 危願 螳讌 谿谿 危エ覲企 覲企 蟆 . 伎ろ企. 手 螻 苦.. 願 麹 讌ル化企.) れ るゼ 覲伎.
--MSSQL2k, pubs..titles SELECT type , MAX(price) MaxPrice FROM titles GROUP BY type --蟆郁骸 type MaxPrice ------------ --------------------- business 19.9900 mod_cook 19.9900 popular_comp 22.9500 psychology 21.5900 trad_cook 20.9500 UNDECIDED NULL 襷 覿 蟆郁骸 title蟾讌 譟壱螻 矩る 一Г蟆瑚? 豐覲企れ 覿覈 れ螻 螳 SQL 燕 蟆企. 蠏碁Μ螻 覓碁 襷讌 る 覃語襯 覲願 覯 る 蟆企.
--Error!! SELECT type , title , MAX(price) MaxPrice FROM titles GROUP BY type -- 蟆郁骸螳 SELECT type , title , MAX(price) MaxPrice FROM titles GROUP BY type , title 蠏碁 企至 讌? 覿れ 螻覩狩企慨. (襷 覈襯企 る れ るゼ 覲願鍵 覃一願 螻覩狩 覺狩. 蠏碁 るレ 企. 蠏碁Μ螻 .)
--焔レ 蟲讌 一碁蓋る 譬讌 . 讌襷 一危郁 伎 れ伎 蟆 蟾... 蟯 . --襷 焔リ讌 螻るゼ る るジ 螻覩殊 伎 蟆企. -- 覦願鹸 讌襷 危企ゼ 蠍 蟆企 蠏碁 覺譴~ SELECT B.type , A.title , B.MaxPrice FROM titles A INNER JOIN ( SELECT type , MAX(price) MaxPrice FROM titles GROUP BY type) B ON A.type = B.type AND A.price = B.MaxPrice --蟆郁骸 type title MaxPrice ------------ -------------------------------------------------------------------------------- --------------------- trad_cook Onions, Leeks, AND Garlic: Cooking Secrets of the Mediterranean 20.9500 psychology Computer Phobic AND Non-Phobic Individuals: Behavior Variations 21.5900 popular_comp But IS It User Friendly? 22.9500 mod_cook Silicon Valley Gastronomic Treats 19.9900 business The Busy Executive's Database Guide 19.9900 business Straight Talk About Computers [edit]
3 DB覈碁 讌 螻覦 #一危磯碁 讌 螻覦 螳 讌 襯 螳覃 所 . 襯 れ 覲伎.
覯讌碁 '' 覲伎. '' 螳 る 伎蠍一 磯 蠏朱企 A 覃 蟆朱 覲 . 蠏碁覃 B 蟆 蟾襴 螻, 伎 企ル 覃, 覯 讌覲伎 豌伎 蠍 蟆谿 覦螻殊ル 覯譯殊 蟆 .
伎 一危 覈碁 襷る誤 襯 伎 . 覓朱 一危 覈碁訖襷 語 Life Cycle 覈 覈 蟆 譬. 襷 一危 覈碁 豈 '覈'襯 瑚 伎螳 覦襦 企 伎企. 覈 螳 語伎 . れ 襴ろれ 覈 企.
覲企 蟾 螻 矩る 襴ろれ '覯譯朱 覈襦' 豢豌.
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磯襴殊 覦蟾 れ 讌 襷豪朱 磯手 . り 殊 り れる 蟆一伎 . (螻轟 蟲覃螳蟆 讌碁 襷蟇磯 豌譴) |