Video: Kuv puas tuaj yeem siv qhov sib txawv nrog ntau kab?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Cov DISTINCT lus ua tau ua siv ntawm ib lossis ntau dua kab ntawm ib lub rooj. table_name; Hauv nqe lus no, qhov tseem ceeb hauv kem_1 kem yog siv los soj ntsuam cov duplicate. Yog koj qhia ntau kab , cov DISTINCT lus yuav ntsuam xyuas qhov duplicate raws li kev sib xyaw ua ke ntawm qhov tseem ceeb ntawm cov no kab.
Hauv qhov no, peb puas tuaj yeem siv qhov txawv ntawm ntau kab hauv SQL?
DISTINCT ntawm ntau kab . Hauv SQL ntau qhov chaw kuj tseem yuav ntxiv nrog DISTINCT lus. DISTINCT yuav tshem tawm cov kab uas txhua tus xaiv teb zoo ib yam.
Ib sab saum toj no, kuv yuav xaiv ntau kab hauv SQL li cas? Rau xaiv ntau kab los ntawm ib lub rooj, tsuas yog cais cov kem npe commas! Piv txwv li, qhov no nug xaiv ob kab , lub npe thiab hnub yug, los ntawm cov neeg lub rooj: Xaiv npe, hnub yug los ntawm cov neeg; Qee zaum, koj yuav xav tau xaiv tag nrho kab los ntawm ib lub rooj.
Yog li ntawd, qhov sib txawv puas siv tau rau txhua kab?
Cov DISTINCT lo lus tseem ceeb yog siv rau txhua kab . Nws txhais tau tias cov lus nug yuav siv qhov sib xyaw ua ke ntawm cov txiaj ntsig hauv txhua kab los ntsuas qhov txawv. Yog koj xav xaiv txawv muaj nuj nqis ntawm ib co kab hauv cov npe xaiv, koj yuav tsum siv GROUP BY clause.
Kuv yuav xaiv cov ntaub ntawv li cas yam tsis muaj duplicates hauv ib kem hauv SQL?
Lub ntsiab tseem ceeb ua kom lub rooj tsis muaj duplicate kab . Txawm li cas los xij, thaum koj siv lub Xaiv nqe lus nug ib feem ntawm lub kab hauv a rooj, koj yuav tau duplicates . rooj 1; Yog koj siv ib kem tom qab tus neeg teb xov tooj DISTINCT, lub database system siv qhov ntawd kem ntsuas luam tawm.
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